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 $186.27   10.545%   $205.9122   $205.91   $205.90   $205.90  
  Purchase #2 $183.65   8.557%   $199.3649   $199.36   $199.35   $199.40  
  Purchase #3 $13.92   4.513%   $14.5482   $14.55   $14.55   $14.50  
  Purchase #4 $89.92   4.427%   $93.9008   $93.90   $93.90   $93.90  
  Purchase #5 $92.42   5.728%   $97.7138   $97.71   $97.70   $97.70  
  Purchase #6 $215.52   13.449%   $244.5053   $244.51   $244.50   $244.50  
  Purchase #7 $127.55   9.523%   $139.6966   $139.70   $139.70   $139.70  
  7 purchase totals = $909.25       $995.6418   $995.64   $995.60   $995.60