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 $212.76   6.419%   $226.4171   $226.42   $226.40   $226.40  
  Purchase #2 $116.95   4.664%   $122.4045   $122.40   $122.40   $122.40  
  Purchase #3 $137.79   9.605%   $151.0247   $151.02   $151.00   $151.00  
  Purchase #4 $178.26   4.664%   $186.574   $186.57   $186.55   $186.60  
  Purchase #5 $125.92   12.632%   $141.8262   $141.83   $141.85   $141.80  
  Purchase #6 $52.82   5.815%   $55.8915   $55.89   $55.90   $55.90  
  Purchase #7 $101.49   12.567%   $114.2442   $114.24   $114.25   $114.20  
  7 purchase totals = $925.99       $998.3822   $998.37   $998.35   $998.30