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 $201.25   13.660%   $228.7408   $228.74   $228.75   $228.70  
  Purchase #2 $90.56   7.355%   $97.2207   $97.22   $97.20   $97.20  
  Purchase #3 $155.30   12.529%   $174.7575   $174.76   $174.75   $174.80  
  Purchase #4 $246.55   3.506%   $255.194   $255.19   $255.20   $255.20  
  Purchase #5 $88.94   4.295%   $92.76   $92.76   $92.75   $92.80  
  Purchase #6 $122.53   12.318%   $137.6232   $137.62   $137.60   $137.60  
  Purchase #7 $42.94   10.326%   $47.374   $47.37   $47.35   $47.40  
  7 purchase totals = $948.07       $1,033.6702   $1,033.66   $1,033.60   $1,033.70