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 $96.33   6.136%   $102.2408   $102.24   $102.25   $102.20  
  Purchase #2 $87.64   10.621%   $96.9482   $96.95   $96.95   $96.90  
  Purchase #3 $17.41   10.473%   $19.2333   $19.23   $19.25   $19.20  
  Purchase #4 $170.73   8.874%   $185.8806   $185.88   $185.90   $185.90  
  Purchase #5 $109.41   8.214%   $118.3969   $118.40   $118.40   $118.40  
  Purchase #6 $200.25   8.622%   $217.5156   $217.52   $217.50   $217.50  
  Purchase #7 $119.64   5.378%   $126.0742   $126.07   $126.05   $126.10  
  7 purchase totals = $801.41       $866.2896   $866.29   $866.30   $866.20