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 $63.63   4.718%   $66.6321   $66.63   $66.65   $66.60  
  Purchase #2 $87.73   9.658%   $96.203   $96.20   $96.20   $96.20  
  Purchase #3 $73.44   8.588%   $79.747   $79.75   $79.75   $79.70  
  Purchase #4 $12.98   11.601%   $14.4858   $14.49   $14.50   $14.50  
  Purchase #5 $5.74   3.467%   $5.939   $5.94   $5.95   $5.90  
  Purchase #6 $239.27   13.348%   $271.2078   $271.21   $271.20   $271.20  
  Purchase #7 $52.84   13.681%   $60.069   $60.07   $60.05   $60.10  
  7 purchase totals = $535.63       $594.2837   $594.29   $594.30   $594.20