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 $88.32   8.116%   $95.4881   $95.49   $95.50   $95.50  
  Purchase #2 $61.82   7.313%   $66.3409   $66.34   $66.35   $66.30  
  Purchase #3 $21.93   12.499%   $24.671   $24.67   $24.65   $24.70  
  Purchase #4 $225.81   13.119%   $255.434   $255.43   $255.45   $255.40  
  Purchase #5 $107.60   6.825%   $114.9437   $114.94   $114.95   $114.90  
  Purchase #6 $43.25   6.771%   $46.1785   $46.18   $46.20   $46.20  
  Purchase #7 $110.46   7.621%   $118.8782   $118.88   $118.90   $118.90  
  7 purchase totals = $659.19       $721.9344   $721.93   $722.00   $721.90