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 $65.92   13.723%   $74.9662   $74.97   $74.95   $75.00  
  Purchase #2 $117.29   10.818%   $129.9784   $129.98   $130.00   $130.00  
  Purchase #3 $248.99   11.117%   $276.6702   $276.67   $276.65   $276.70  
  Purchase #4 $240.69   5.228%   $253.2733   $253.27   $253.25   $253.30  
  Purchase #5 $32.95   9.241%   $35.9949   $35.99   $36.00   $36.00  
  Purchase #6 $129.56   11.559%   $144.5358   $144.54   $144.55   $144.50  
  Purchase #7 $55.49   4.568%   $58.0248   $58.02   $58.00   $58.00  
  7 purchase totals = $890.89       $973.4436   $973.44   $973.40   $973.50