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 $57.83   8.147%   $62.5414   $62.54   $62.55   $62.50  
  Purchase #2 $195.78   4.314%   $204.2259   $204.23   $204.25   $204.20  
  Purchase #3 $158.31   7.739%   $170.5616   $170.56   $170.55   $170.60  
  Purchase #4 $227.95   7.201%   $244.3647   $244.36   $244.35   $244.40  
  Purchase #5 $113.71   12.530%   $127.9579   $127.96   $127.95   $128.00  
  Purchase #6 $197.39   9.280%   $215.7078   $215.71   $215.70   $215.70  
  Purchase #7 $193.26   11.504%   $215.4926   $215.49   $215.50   $215.50  
  7 purchase totals = $1,144.23       $1,240.8519   $1,240.85   $1,240.85   $1,240.90