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 $47.87   12.427%   $53.8188   $53.82   $53.80   $53.80  
  Purchase #2 $111.65   11.211%   $124.1671   $124.17   $124.15   $124.20  
  Purchase #3 $143.81   8.671%   $156.2798   $156.28   $156.30   $156.30  
  Purchase #4 $239.40   11.637%   $267.259   $267.26   $267.25   $267.30  
  Purchase #5 $66.42   7.290%   $71.262   $71.26   $71.25   $71.30  
  Purchase #6 $156.85   12.759%   $176.8625   $176.86   $176.85   $176.90  
  Purchase #7 $97.54   7.113%   $104.478   $104.48   $104.50   $104.50  
  7 purchase totals = $863.54       $954.1272   $954.13   $954.10   $954.30