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 $229.67   3.181%   $236.9758   $236.98   $237.00   $237.00  
  Purchase #2 $69.49   9.574%   $76.143   $76.14   $76.15   $76.10  
  Purchase #3 $23.68   8.389%   $25.6665   $25.67   $25.65   $25.70  
  Purchase #4 $130.60   5.647%   $137.975   $137.98   $138.00   $138.00  
  Purchase #5 $179.59   3.790%   $186.3965   $186.40   $186.40   $186.40  
  Purchase #6 $171.35   13.655%   $194.7478   $194.75   $194.75   $194.70  
  Purchase #7 $215.27   10.794%   $238.5062   $238.51   $238.50   $238.50  
  7 purchase totals = $1,019.65       $1,096.4108   $1,096.43   $1,096.45   $1,096.40