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 $23.97   9.723%   $26.3006   $26.30   $26.30   $26.30  
  Purchase #2 $129.34   10.719%   $143.204   $143.20   $143.20   $143.20  
  Purchase #3 $169.28   8.605%   $183.8465   $183.85   $183.85   $183.80  
  Purchase #4 $155.70   4.612%   $162.8809   $162.88   $162.90   $162.90  
  Purchase #5 $53.77   8.378%   $58.2749   $58.27   $58.25   $58.30  
  Purchase #6 $109.53   9.827%   $120.2935   $120.29   $120.30   $120.30  
  Purchase #7 $244.41   7.638%   $263.078   $263.08   $263.10   $263.10  
  7 purchase totals = $886.00       $957.8784   $957.87   $957.90   $957.90