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 $57.76   11.614%   $64.4682   $64.47   $64.45   $64.50  
  Purchase #2 $146.86   8.235%   $158.9539   $158.95   $158.95   $159.00  
  Purchase #3 $229.88   9.234%   $251.1071   $251.11   $251.10   $251.10  
  Purchase #4 $151.57   6.755%   $161.8086   $161.81   $161.80   $161.80  
  Purchase #5 $136.29   4.441%   $142.3426   $142.34   $142.35   $142.30  
  Purchase #6 $239.25   5.324%   $251.9877   $251.99   $252.00   $252.00  
  Purchase #7 $168.37   4.638%   $176.179   $176.18   $176.20   $176.20  
  7 purchase totals = $1,129.98       $1,206.8471   $1,206.85   $1,206.85   $1,206.90