Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $240.31   11.809%   $268.6882   $268.69   $268.70   $268.70  
  Purchase #2 $211.62   12.860%   $238.8343   $238.83   $238.85   $238.80  
  Purchase #3 $205.91   13.823%   $234.3729   $234.37   $234.35   $234.40  
  Purchase #4 $237.27   11.657%   $264.9286   $264.93   $264.95   $264.90  
  Purchase #5 $241.58   11.187%   $268.6056   $268.61   $268.60   $268.60  
  Purchase #6 $96.66   13.827%   $110.0252   $110.03   $110.05   $110.00  
  Purchase #7 $135.27   11.851%   $151.3008   $151.30   $151.30   $151.30  
  7 purchase totals = $1,368.62       $1,536.7556   $1,536.76   $1,536.80   $1,536.70