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 $30.52   10.167%   $33.623   $33.62   $33.60   $33.60  
  Purchase #2 $106.62   5.355%   $112.3295   $112.33   $112.35   $112.30  
  Purchase #3 $237.77   9.534%   $260.439   $260.44   $260.45   $260.40  
  Purchase #4 $132.53   4.581%   $138.6012   $138.60   $138.60   $138.60  
  Purchase #5 $170.49   10.803%   $188.908   $188.91   $188.90   $188.90  
  Purchase #6 $25.26   11.151%   $28.0767   $28.08   $28.10   $28.10  
  Purchase #7 $170.53   12.315%   $191.5308   $191.53   $191.55   $191.50  
  7 purchase totals = $873.72       $953.5082   $953.51   $953.55   $953.40