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 $54.67   10.293%   $60.2972   $60.30   $60.30   $60.30  
  Purchase #2 $92.82   8.541%   $100.7478   $100.75   $100.75   $100.70  
  Purchase #3 $230.57   9.131%   $251.6233   $251.62   $251.60   $251.60  
  Purchase #4 $109.81   3.517%   $113.672   $113.67   $113.65   $113.70  
  Purchase #5 $127.46   10.684%   $141.0778   $141.08   $141.10   $141.10  
  Purchase #6 $79.50   5.135%   $83.5823   $83.58   $83.60   $83.60  
  Purchase #7 $206.82   13.420%   $234.5752   $234.58   $234.60   $234.60  
  7 purchase totals = $901.65       $985.5756   $985.58   $985.60   $985.60