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 $248.77   7.535%   $267.5148   $267.51   $267.50   $267.50  
  Purchase #2 $159.30   10.650%   $176.2655   $176.27   $176.25   $176.30  
  Purchase #3 $106.64   4.689%   $111.6403   $111.64   $111.65   $111.60  
  Purchase #4 $51.82   3.710%   $53.7425   $53.74   $53.75   $53.70  
  Purchase #5 $155.54   5.567%   $164.1989   $164.20   $164.20   $164.20  
  Purchase #6 $44.55   13.499%   $50.5638   $50.56   $50.55   $50.60  
  Purchase #7 $93.80   11.661%   $104.738   $104.74   $104.75   $104.70  
  7 purchase totals = $860.42       $928.6638   $928.66   $928.65   $928.60