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 $246.42   3.868%   $255.9515   $255.95   $255.95   $256.00  
  Purchase #2 $225.43   4.841%   $236.3431   $236.34   $236.35   $236.30  
  Purchase #3 $101.78   5.768%   $107.6507   $107.65   $107.65   $107.70  
  Purchase #4 $53.34   6.212%   $56.6535   $56.65   $56.65   $56.70  
  Purchase #5 $68.26   8.602%   $74.1317   $74.13   $74.15   $74.10  
  Purchase #6 $233.58   9.496%   $255.7608   $255.76   $255.75   $255.80  
  Purchase #7 $29.65   9.215%   $32.3822   $32.38   $32.40   $32.40  
  7 purchase totals = $958.46       $1,018.8735   $1,018.86   $1,018.90   $1,019.00