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 $90.63   9.753%   $99.4691   $99.47   $99.45   $99.50  
  Purchase #2 $120.40   13.247%   $136.3494   $136.35   $136.35   $136.30  
  Purchase #3 $156.37   5.506%   $164.9797   $164.98   $165.00   $165.00  
  Purchase #4 $247.45   7.601%   $266.2587   $266.26   $266.25   $266.30  
  Purchase #5 $191.70   7.588%   $206.2462   $206.25   $206.25   $206.20  
  Purchase #6 $44.80   8.448%   $48.5847   $48.58   $48.60   $48.60  
  Purchase #7 $92.92   10.136%   $102.3384   $102.34   $102.35   $102.30  
  7 purchase totals = $944.27       $1,024.2262   $1,024.23   $1,024.25   $1,024.20