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 $92.89   6.217%   $98.665   $98.67   $98.65   $98.70  
  Purchase #2 $216.90   3.606%   $224.7214   $224.72   $224.70   $224.70  
  Purchase #3 $71.29   13.750%   $81.0924   $81.09   $81.10   $81.10  
  Purchase #4 $103.29   5.460%   $108.9296   $108.93   $108.95   $108.90  
  Purchase #5 $164.92   11.432%   $183.7737   $183.77   $183.75   $183.80  
  Purchase #6 $151.51   5.224%   $159.4249   $159.42   $159.40   $159.40  
  Purchase #7 $79.33   5.824%   $83.9502   $83.95   $83.95   $84.00  
  7 purchase totals = $880.13       $940.5572   $940.55   $940.50   $940.60