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 $60.55   7.691%   $65.2069   $65.21   $65.20   $65.20  
  Purchase #2 $99.34   5.393%   $104.6974   $104.70   $104.70   $104.70  
  Purchase #3 $200.67   7.367%   $215.4534   $215.45   $215.45   $215.50  
  Purchase #4 $60.75   6.723%   $64.8342   $64.83   $64.85   $64.80  
  Purchase #5 $182.86   6.570%   $194.8739   $194.87   $194.85   $194.90  
  Purchase #6 $84.61   4.339%   $88.2812   $88.28   $88.30   $88.30  
  Purchase #7 $75.87   5.133%   $79.7644   $79.76   $79.75   $79.80  
  7 purchase totals = $764.65       $813.1114   $813.10   $813.10   $813.20