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 $87.46   11.745%   $97.7322   $97.73   $97.75   $97.70  
  Purchase #2 $118.91   4.852%   $124.6795   $124.68   $124.70   $124.70  
  Purchase #3 $229.98   7.189%   $246.5133   $246.51   $246.50   $246.50  
  Purchase #4 $145.62   4.228%   $151.7768   $151.78   $151.80   $151.80  
  Purchase #5 $119.81   11.635%   $133.7499   $133.75   $133.75   $133.70  
  Purchase #6 $227.69   5.486%   $240.1811   $240.18   $240.20   $240.20  
  Purchase #7 $5.83   8.821%   $6.3443   $6.34   $6.35   $6.30  
  7 purchase totals = $935.30       $1,000.9771   $1,000.97   $1,001.05   $1,000.90