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 $176.80   7.824%   $190.6328   $190.63   $190.65   $190.60  
  Purchase #2 $66.41   10.407%   $73.3213   $73.32   $73.30   $73.30  
  Purchase #3 $195.70   5.705%   $206.8647   $206.86   $206.85   $206.90  
  Purchase #4 $199.33   4.839%   $208.9756   $208.98   $209.00   $209.00  
  Purchase #5 $91.82   11.735%   $102.5951   $102.60   $102.60   $102.60  
  Purchase #6 $247.43   3.428%   $255.9119   $255.91   $255.90   $255.90  
  Purchase #7 $202.91   6.203%   $215.4965   $215.50   $215.50   $215.50  
  7 purchase totals = $1,180.40       $1,253.7979   $1,253.80   $1,253.80   $1,253.80