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 $56.79   5.774%   $60.0691   $60.07   $60.05   $60.10  
  Purchase #2 $66.96   12.401%   $75.2637   $75.26   $75.25   $75.30  
  Purchase #3 $71.76   3.201%   $74.057   $74.06   $74.05   $74.10  
  Purchase #4 $237.49   10.227%   $261.7781   $261.78   $261.80   $261.80  
  Purchase #5 $154.97   5.868%   $164.0636   $164.06   $164.05   $164.10  
  Purchase #6 $116.75   3.839%   $121.232   $121.23   $121.25   $121.20  
  Purchase #7 $55.65   7.566%   $59.8605   $59.86   $59.85   $59.90  
  7 purchase totals = $760.37       $816.3240   $816.32   $816.30   $816.50