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 $73.37   4.524%   $76.6893   $76.69   $76.70   $76.70  
  Purchase #2 $116.84   3.738%   $121.2075   $121.21   $121.20   $121.20  
  Purchase #3 $145.29   4.266%   $151.4881   $151.49   $151.50   $151.50  
  Purchase #4 $164.74   11.350%   $183.438   $183.44   $183.45   $183.40  
  Purchase #5 $14.86   10.275%   $16.3869   $16.39   $16.40   $16.40  
  Purchase #6 $115.75   5.143%   $121.703   $121.70   $121.70   $121.70  
  Purchase #7 $248.65   12.731%   $280.3056   $280.31   $280.30   $280.30  
  7 purchase totals = $879.50       $951.2184   $951.23   $951.25   $951.20