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 $64.46   4.852%   $67.5876   $67.59   $67.60   $67.60  
  Purchase #2 $185.84   12.368%   $208.8247   $208.82   $208.80   $208.80  
  Purchase #3 $79.34   11.750%   $88.6625   $88.66   $88.65   $88.70  
  Purchase #4 $249.50   8.713%   $271.2389   $271.24   $271.25   $271.20  
  Purchase #5 $155.42   10.375%   $171.5448   $171.54   $171.55   $171.50  
  Purchase #6 $34.73   5.373%   $36.596   $36.60   $36.60   $36.60  
  Purchase #7 $21.32   6.481%   $22.7017   $22.70   $22.70   $22.70  
  7 purchase totals = $790.61       $867.1562   $867.15   $867.15   $867.10