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 $66.50   13.124%   $75.2275   $75.23   $75.25   $75.20  
  Purchase #2 $161.52   8.830%   $175.7822   $175.78   $175.80   $175.80  
  Purchase #3 $24.52   4.480%   $25.6185   $25.62   $25.60   $25.60  
  Purchase #4 $167.97   7.593%   $180.724   $180.72   $180.70   $180.70  
  Purchase #5 $210.49   11.695%   $235.1068   $235.11   $235.10   $235.10  
  Purchase #6 $49.37   13.249%   $55.911   $55.91   $55.90   $55.90  
  Purchase #7 $234.86   5.559%   $247.9159   $247.92   $247.90   $247.90  
  7 purchase totals = $915.23       $996.2859   $996.29   $996.25   $996.20