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 $34.76   4.714%   $36.3986   $36.40   $36.40   $36.40  
  Purchase #2 $224.81   7.540%   $241.7607   $241.76   $241.75   $241.80  
  Purchase #3 $58.53   8.545%   $63.5314   $63.53   $63.55   $63.50  
  Purchase #4 $130.94   11.788%   $146.3752   $146.38   $146.40   $146.40  
  Purchase #5 $68.44   5.543%   $72.2336   $72.23   $72.25   $72.20  
  Purchase #6 $97.79   11.185%   $108.7278   $108.73   $108.75   $108.70  
  Purchase #7 $228.37   7.506%   $245.5115   $245.51   $245.50   $245.50  
  7 purchase totals = $843.64       $914.5388   $914.54   $914.60   $914.50