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 $209.87   11.760%   $234.5507   $234.55   $234.55   $234.60  
  Purchase #2 $142.54   10.162%   $157.0249   $157.02   $157.00   $157.00  
  Purchase #3 $244.38   5.613%   $258.097   $258.10   $258.10   $258.10  
  Purchase #4 $68.66   5.306%   $72.3031   $72.30   $72.30   $72.30  
  Purchase #5 $188.83   3.154%   $194.7857   $194.79   $194.80   $194.80  
  Purchase #6 $71.99   6.229%   $76.4743   $76.47   $76.45   $76.50  
  Purchase #7 $10.65   5.830%   $11.2709   $11.27   $11.25   $11.30  
  7 purchase totals = $936.92       $1,004.5066   $1,004.50   $1,004.45   $1,004.60