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 $195.53   8.113%   $211.3933   $211.39   $211.40   $211.40  
  Purchase #2 $74.37   13.575%   $84.4657   $84.47   $84.45   $84.50  
  Purchase #3 $98.88   10.226%   $108.9915   $108.99   $109.00   $109.00  
  Purchase #4 $229.78   8.716%   $249.8076   $249.81   $249.80   $249.80  
  Purchase #5 $248.68   8.747%   $270.432   $270.43   $270.45   $270.40  
  Purchase #6 $217.96   13.741%   $247.9099   $247.91   $247.90   $247.90  
  Purchase #7 $89.85   5.178%   $94.5024   $94.50   $94.50   $94.50  
  7 purchase totals = $1,155.05       $1,267.5024   $1,267.50   $1,267.50   $1,267.50