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 $66.58   13.176%   $75.3526   $75.35   $75.35   $75.40  
  Purchase #2 $232.82   9.812%   $255.6643   $255.66   $255.65   $255.70  
  Purchase #3 $182.62   6.677%   $194.8135   $194.81   $194.80   $194.80  
  Purchase #4 $80.79   10.791%   $89.508   $89.51   $89.50   $89.50  
  Purchase #5 $221.54   11.822%   $247.7305   $247.73   $247.75   $247.70  
  Purchase #6 $32.38   5.786%   $34.2535   $34.25   $34.25   $34.30  
  Purchase #7 $128.49   5.138%   $135.0918   $135.09   $135.10   $135.10  
  7 purchase totals = $945.22       $1,032.4142   $1,032.40   $1,032.40   $1,032.50