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 $162.96   11.696%   $182.0198   $182.02   $182.00   $182.00  
  Purchase #2 $219.41   11.298%   $244.1989   $244.20   $244.20   $244.20  
  Purchase #3 $101.86   13.424%   $115.5337   $115.53   $115.55   $115.50  
  Purchase #4 $113.54   6.778%   $121.2357   $121.24   $121.25   $121.20  
  Purchase #5 $206.89   5.605%   $218.4862   $218.49   $218.50   $218.50  
  Purchase #6 $250.61   4.651%   $262.2659   $262.27   $262.25   $262.30  
  Purchase #7 $215.71   11.140%   $239.7401   $239.74   $239.75   $239.70  
  7 purchase totals = $1,270.98       $1,383.4803   $1,383.49   $1,383.50   $1,383.40