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 $76.94   9.122%   $83.9585   $83.96   $83.95   $84.00  
  Purchase #2 $165.81   6.725%   $176.9607   $176.96   $176.95   $177.00  
  Purchase #3 $112.39   12.788%   $126.7624   $126.76   $126.75   $126.80  
  Purchase #4 $107.82   8.794%   $117.3017   $117.30   $117.30   $117.30  
  Purchase #5 $140.66   13.601%   $159.7912   $159.79   $159.80   $159.80  
  Purchase #6 $148.59   4.478%   $155.2439   $155.24   $155.25   $155.20  
  Purchase #7 $161.94   8.439%   $175.6061   $175.61   $175.60   $175.60  
  7 purchase totals = $914.15       $995.6245   $995.62   $995.60   $995.70