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 $124.86   13.116%   $141.2366   $141.24   $141.25   $141.20  
  Purchase #2 $14.31   11.213%   $15.9146   $15.91   $15.90   $15.90  
  Purchase #3 $53.56   10.104%   $58.9717   $58.97   $58.95   $59.00  
  Purchase #4 $71.88   11.568%   $80.1951   $80.20   $80.20   $80.20  
  Purchase #5 $226.99   7.688%   $244.441   $244.44   $244.45   $244.40  
  Purchase #6 $23.81   12.672%   $26.8272   $26.83   $26.85   $26.80  
  Purchase #7 $173.38   8.287%   $187.748   $187.75   $187.75   $187.70  
  7 purchase totals = $688.79       $755.3342   $755.34   $755.35   $755.20