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 $76.97   11.139%   $85.5437   $85.54   $85.55   $85.50  
  Purchase #2 $22.44   8.219%   $24.2843   $24.28   $24.30   $24.30  
  Purchase #3 $98.56   7.801%   $106.2487   $106.25   $106.25   $106.20  
  Purchase #4 $114.76   3.636%   $118.9327   $118.93   $118.95   $118.90  
  Purchase #5 $205.26   6.808%   $219.2341   $219.23   $219.25   $219.20  
  Purchase #6 $227.76   9.578%   $249.5749   $249.57   $249.55   $249.60  
  Purchase #7 $104.28   7.692%   $112.3012   $112.30   $112.30   $112.30  
  7 purchase totals = $850.03       $916.1196   $916.10   $916.15   $916.00