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 $58.28   10.245%   $64.2508   $64.25   $64.25   $64.30  
  Purchase #2 $208.27   4.410%   $217.4547   $217.45   $217.45   $217.50  
  Purchase #3 $152.74   13.873%   $173.9296   $173.93   $173.95   $173.90  
  Purchase #4 $191.74   12.467%   $215.6442   $215.64   $215.65   $215.60  
  Purchase #5 $180.62   13.291%   $204.6262   $204.63   $204.65   $204.60  
  Purchase #6 $244.67   13.279%   $277.1597   $277.16   $277.15   $277.20  
  Purchase #7 $217.69   5.274%   $229.171   $229.17   $229.15   $229.20  
  7 purchase totals = $1,254.01       $1,382.2362   $1,382.23   $1,382.25   $1,382.30