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 $82.78   11.440%   $92.25   $92.25   $92.25   $92.30  
  Purchase #2 $108.26   7.830%   $116.7368   $116.74   $116.75   $116.70  
  Purchase #3 $161.30   4.396%   $168.3907   $168.39   $168.40   $168.40  
  Purchase #4 $215.35   8.340%   $233.3102   $233.31   $233.30   $233.30  
  Purchase #5 $32.58   7.323%   $34.9658   $34.97   $34.95   $35.00  
  Purchase #6 $105.42   3.332%   $108.9326   $108.93   $108.95   $108.90  
  Purchase #7 $112.72   5.622%   $119.0571   $119.06   $119.05   $119.10  
  7 purchase totals = $818.41       $873.6432   $873.65   $873.65   $873.70