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 $37.50   10.820%   $41.5575   $41.56   $41.55   $41.60  
  Purchase #2 $212.50   5.778%   $224.7783   $224.78   $224.80   $224.80  
  Purchase #3 $123.63   5.280%   $130.1577   $130.16   $130.15   $130.20  
  Purchase #4 $155.38   11.853%   $173.7972   $173.80   $173.80   $173.80  
  Purchase #5 $238.69   8.214%   $258.296   $258.30   $258.30   $258.30  
  Purchase #6 $91.34   11.172%   $101.5445   $101.54   $101.55   $101.50  
  Purchase #7 $38.40   6.827%   $41.0216   $41.02   $41.00   $41.00  
  7 purchase totals = $897.44       $971.1528   $971.16   $971.15   $971.20