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 $59.25   11.831%   $66.2599   $66.26   $66.25   $66.30  
  Purchase #2 $216.93   5.406%   $228.6572   $228.66   $228.65   $228.70  
  Purchase #3 $28.92   3.662%   $29.9791   $29.98   $30.00   $30.00  
  Purchase #4 $89.58   12.738%   $100.9907   $100.99   $101.00   $101.00  
  Purchase #5 $66.95   7.840%   $72.1989   $72.20   $72.20   $72.20  
  Purchase #6 $230.63   12.636%   $259.7724   $259.77   $259.75   $259.80  
  Purchase #7 $78.73   9.501%   $86.2101   $86.21   $86.20   $86.20  
  7 purchase totals = $770.99       $844.0683   $844.07   $844.05   $844.20