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 $197.63   8.779%   $214.9799   $214.98   $215.00   $215.00  
  Purchase #2 $64.37   7.275%   $69.0529   $69.05   $69.05   $69.10  
  Purchase #3 $220.38   8.196%   $238.4423   $238.44   $238.45   $238.40  
  Purchase #4 $47.81   3.860%   $49.6555   $49.66   $49.65   $49.70  
  Purchase #5 $238.36   7.566%   $256.3943   $256.39   $256.40   $256.40  
  Purchase #6 $124.76   10.275%   $137.5791   $137.58   $137.60   $137.60  
  Purchase #7 $98.60   7.836%   $106.3263   $106.33   $106.35   $106.30  
  7 purchase totals = $991.91       $1,072.4303   $1,072.43   $1,072.50   $1,072.50