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 $52.68   12.556%   $59.2945   $59.29   $59.30   $59.30  
  Purchase #2 $94.99   11.356%   $105.7771   $105.78   $105.80   $105.80  
  Purchase #3 $98.64   13.750%   $112.203   $112.20   $112.20   $112.20  
  Purchase #4 $32.78   3.328%   $33.8709   $33.87   $33.85   $33.90  
  Purchase #5 $205.87   11.805%   $230.173   $230.17   $230.15   $230.20  
  Purchase #6 $236.36   10.263%   $260.6176   $260.62   $260.60   $260.60  
  Purchase #7 $145.76   5.843%   $154.2768   $154.28   $154.30   $154.30  
  7 purchase totals = $867.08       $956.2129   $956.21   $956.20   $956.30