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 $208.59   11.574%   $232.7322   $232.73   $232.75   $232.70  
  Purchase #2 $146.28   9.319%   $159.9118   $159.91   $159.90   $159.90  
  Purchase #3 $145.73   8.869%   $158.6548   $158.65   $158.65   $158.70  
  Purchase #4 $169.94   3.677%   $176.1887   $176.19   $176.20   $176.20  
  Purchase #5 $224.39   9.519%   $245.7497   $245.75   $245.75   $245.70  
  Purchase #6 $140.99   12.750%   $158.9662   $158.97   $158.95   $159.00  
  Purchase #7 $110.50   11.727%   $123.4583   $123.46   $123.45   $123.50  
  7 purchase totals = $1,146.42       $1,255.6617   $1,255.66   $1,255.65   $1,255.70