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 $128.36   7.201%   $137.6032   $137.60   $137.60   $137.60  
  Purchase #2 $189.97   13.466%   $215.5514   $215.55   $215.55   $215.60  
  Purchase #3 $68.60   7.568%   $73.7916   $73.79   $73.80   $73.80  
  Purchase #4 $44.84   9.626%   $49.1563   $49.16   $49.15   $49.20  
  Purchase #5 $57.59   12.215%   $64.6246   $64.62   $64.60   $64.60  
  Purchase #6 $165.28   10.399%   $182.4675   $182.47   $182.45   $182.50  
  Purchase #7 $220.73   10.686%   $244.3172   $244.32   $244.30   $244.30  
  7 purchase totals = $875.37       $967.5118   $967.51   $967.45   $967.60