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 $68.69   11.778%   $76.7803   $76.78   $76.80   $76.80  
  Purchase #2 $136.41   9.112%   $148.8397   $148.84   $148.85   $148.80  
  Purchase #3 $154.75   5.396%   $163.1003   $163.10   $163.10   $163.10  
  Purchase #4 $107.57   8.481%   $116.693   $116.69   $116.70   $116.70  
  Purchase #5 $47.57   7.782%   $51.2719   $51.27   $51.25   $51.30  
  Purchase #6 $213.45   11.207%   $237.3713   $237.37   $237.35   $237.40  
  Purchase #7 $117.54   5.871%   $124.4408   $124.44   $124.45   $124.40  
  7 purchase totals = $845.98       $918.4973   $918.49   $918.50   $918.50