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 $117.48   6.742%   $125.4005   $125.40   $125.40   $125.40  
  Purchase #2 $236.46   8.583%   $256.7554   $256.76   $256.75   $256.80  
  Purchase #3 $84.58   3.560%   $87.591   $87.59   $87.60   $87.60  
  Purchase #4 $132.47   8.491%   $143.718   $143.72   $143.70   $143.70  
  Purchase #5 $17.62   8.720%   $19.1565   $19.16   $19.15   $19.20  
  Purchase #6 $207.82   8.740%   $225.9835   $225.98   $226.00   $226.00  
  Purchase #7 $88.33   9.847%   $97.0279   $97.03   $97.05   $97.00  
  7 purchase totals = $884.76       $955.6328   $955.64   $955.65   $955.70