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 $58.88   5.164%   $61.9206   $61.92   $61.90   $61.90  
  Purchase #2 $205.63   13.728%   $233.8589   $233.86   $233.85   $233.90  
  Purchase #3 $43.75   5.450%   $46.1344   $46.13   $46.15   $46.10  
  Purchase #4 $237.65   10.760%   $263.2211   $263.22   $263.20   $263.20  
  Purchase #5 $93.69   6.361%   $99.6496   $99.65   $99.65   $99.60  
  Purchase #6 $75.48   11.752%   $84.3504   $84.35   $84.35   $84.40  
  Purchase #7 $50.32   6.517%   $53.5994   $53.60   $53.60   $53.60  
  7 purchase totals = $765.40       $842.7344   $842.73   $842.70   $842.70