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 $226.54   8.481%   $245.7529   $245.75   $245.75   $245.80  
  Purchase #2 $133.76   3.569%   $138.5339   $138.53   $138.55   $138.50  
  Purchase #3 $209.68   12.791%   $236.5002   $236.50   $236.50   $236.50  
  Purchase #4 $66.96   3.362%   $69.2112   $69.21   $69.20   $69.20  
  Purchase #5 $78.52   8.248%   $84.9963   $85.00   $85.00   $85.00  
  Purchase #6 $170.71   12.154%   $191.4581   $191.46   $191.45   $191.50  
  Purchase #7 $216.81   11.592%   $241.9426   $241.94   $241.95   $241.90  
  7 purchase totals = $1,102.98       $1,208.3952   $1,208.39   $1,208.40   $1,208.40