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 $82.38   6.212%   $87.4974   $87.50   $87.50   $87.50  
  Purchase #2 $143.58   10.743%   $159.0048   $159.00   $159.00   $159.00  
  Purchase #3 $30.71   13.669%   $34.9077   $34.91   $34.90   $34.90  
  Purchase #4 $64.43   9.511%   $70.5579   $70.56   $70.55   $70.60  
  Purchase #5 $84.84   13.199%   $96.038   $96.04   $96.05   $96.00  
  Purchase #6 $124.46   13.533%   $141.3032   $141.30   $141.30   $141.30  
  Purchase #7 $115.77   7.726%   $124.7144   $124.71   $124.70   $124.70  
  7 purchase totals = $646.17       $714.0234   $714.02   $714.00   $714.00