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 $67.70   13.608%   $76.9126   $76.91   $76.90   $76.90  
  Purchase #2 $194.35   7.378%   $208.6891   $208.69   $208.70   $208.70  
  Purchase #3 $100.90   3.108%   $104.036   $104.04   $104.05   $104.00  
  Purchase #4 $29.55   8.526%   $32.0694   $32.07   $32.05   $32.10  
  Purchase #5 $208.60   12.453%   $234.577   $234.58   $234.60   $234.60  
  Purchase #6 $61.34   12.364%   $68.9241   $68.92   $68.90   $68.90  
  Purchase #7 $25.39   5.180%   $26.7052   $26.71   $26.70   $26.70  
  7 purchase totals = $687.83       $751.9134   $751.92   $751.90   $751.90