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 $169.96   12.847%   $191.7948   $191.79   $191.80   $191.80  
  Purchase #2 $157.39   8.411%   $170.6281   $170.63   $170.65   $170.60  
  Purchase #3 $244.44   13.797%   $278.1654   $278.17   $278.15   $278.20  
  Purchase #4 $236.75   12.471%   $266.2751   $266.28   $266.30   $266.30  
  Purchase #5 $61.82   8.450%   $67.0438   $67.04   $67.05   $67.00  
  Purchase #6 $221.69   3.216%   $228.8196   $228.82   $228.80   $228.80  
  Purchase #7 $242.75   7.500%   $260.9563   $260.96   $260.95   $261.00  
  7 purchase totals = $1,334.80       $1,463.6831   $1,463.69   $1,463.70   $1,463.70