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 $248.37   13.465%   $281.813   $281.81   $281.80   $281.80  
  Purchase #2 $107.45   9.507%   $117.6653   $117.67   $117.65   $117.70  
  Purchase #3 $226.62   11.245%   $252.1034   $252.10   $252.10   $252.10  
  Purchase #4 $177.81   9.353%   $194.4406   $194.44   $194.45   $194.40  
  Purchase #5 $14.49   8.160%   $15.6724   $15.67   $15.65   $15.70  
  Purchase #6 $24.30   13.193%   $27.5059   $27.51   $27.50   $27.50  
  Purchase #7 $68.78   9.191%   $75.1016   $75.10   $75.10   $75.10  
  7 purchase totals = $867.82       $964.3022   $964.30   $964.25   $964.30