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 $233.58   12.791%   $263.4572   $263.46   $263.45   $263.50  
  Purchase #2 $232.38   12.373%   $261.1324   $261.13   $261.15   $261.10  
  Purchase #3 $226.89   13.827%   $258.2621   $258.26   $258.25   $258.30  
  Purchase #4 $101.88   5.216%   $107.1941   $107.19   $107.20   $107.20  
  Purchase #5 $46.97   5.154%   $49.3908   $49.39   $49.40   $49.40  
  Purchase #6 $212.73   13.338%   $241.1039   $241.10   $241.10   $241.10  
  Purchase #7 $246.97   9.425%   $270.2469   $270.25   $270.25   $270.20  
  7 purchase totals = $1,301.40       $1,450.7874   $1,450.78   $1,450.80   $1,450.80