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 $46.94   3.378%   $48.5256   $48.53   $48.55   $48.50  
  Purchase #2 $134.49   12.707%   $151.5796   $151.58   $151.60   $151.60  
  Purchase #3 $108.55   12.715%   $122.3521   $122.35   $122.35   $122.40  
  Purchase #4 $243.61   9.775%   $267.4229   $267.42   $267.40   $267.40  
  Purchase #5 $202.25   7.823%   $218.072   $218.07   $218.05   $218.10  
  Purchase #6 $47.70   11.384%   $53.1302   $53.13   $53.15   $53.10  
  Purchase #7 $68.66   7.602%   $73.8795   $73.88   $73.90   $73.90  
  7 purchase totals = $852.20       $934.9619   $934.96   $935.00   $935.00