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 $247.37   5.186%   $260.1986   $260.20   $260.20   $260.20  
  Purchase #2 $16.44   13.666%   $18.6867   $18.69   $18.70   $18.70  
  Purchase #3 $223.65   6.732%   $238.7061   $238.71   $238.70   $238.70  
  Purchase #4 $10.33   7.338%   $11.088   $11.09   $11.10   $11.10  
  Purchase #5 $160.77   5.594%   $169.7635   $169.76   $169.75   $169.80  
  Purchase #6 $117.63   3.428%   $121.6624   $121.66   $121.65   $121.70  
  Purchase #7 $125.66   6.512%   $133.843   $133.84   $133.85   $133.80  
  7 purchase totals = $901.85       $953.9483   $953.95   $953.95   $954.00