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 $29.96   9.351%   $32.7616   $32.76   $32.75   $32.80  
  Purchase #2 $31.76   4.545%   $33.2035   $33.20   $33.20   $33.20  
  Purchase #3 $209.88   8.229%   $227.151   $227.15   $227.15   $227.20  
  Purchase #4 $153.76   3.630%   $159.3415   $159.34   $159.35   $159.30  
  Purchase #5 $192.94   12.210%   $216.498   $216.50   $216.50   $216.50  
  Purchase #6 $64.97   10.769%   $71.9666   $71.97   $71.95   $72.00  
  Purchase #7 $184.66   10.662%   $204.3484   $204.35   $204.35   $204.30  
  7 purchase totals = $867.93       $945.2706   $945.27   $945.25   $945.30