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 $131.29   8.377%   $142.2882   $142.29   $142.30   $142.30  
  Purchase #2 $127.54   7.848%   $137.5493   $137.55   $137.55   $137.50  
  Purchase #3 $119.73   8.207%   $129.5562   $129.56   $129.55   $129.60  
  Purchase #4 $91.25   7.106%   $97.7342   $97.73   $97.75   $97.70  
  Purchase #5 $57.82   9.139%   $63.1042   $63.10   $63.10   $63.10  
  Purchase #6 $223.55   11.610%   $249.5042   $249.50   $249.50   $249.50  
  Purchase #7 $209.51   8.190%   $226.6689   $226.67   $226.65   $226.70  
  7 purchase totals = $960.69       $1,046.4052   $1,046.40   $1,046.40   $1,046.40