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 $207.33   8.158%   $224.244   $224.24   $224.25   $224.20  
  Purchase #2 $166.46   12.635%   $187.4922   $187.49   $187.50   $187.50  
  Purchase #3 $38.58   3.323%   $39.862   $39.86   $39.85   $39.90  
  Purchase #4 $188.98   13.395%   $214.2939   $214.29   $214.30   $214.30  
  Purchase #5 $61.80   3.734%   $64.1076   $64.11   $64.10   $64.10  
  Purchase #6 $15.31   7.113%   $16.399   $16.40   $16.40   $16.40  
  Purchase #7 $177.89   9.608%   $194.9817   $194.98   $195.00   $195.00  
  7 purchase totals = $856.35       $941.3804   $941.37   $941.40   $941.40