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 $59.95   13.388%   $67.9761   $67.98   $68.00   $68.00  
  Purchase #2 $81.87   3.788%   $84.9712   $84.97   $84.95   $85.00  
  Purchase #3 $44.89   7.659%   $48.3281   $48.33   $48.35   $48.30  
  Purchase #4 $51.66   11.294%   $57.4945   $57.49   $57.50   $57.50  
  Purchase #5 $164.74   11.787%   $184.1579   $184.16   $184.15   $184.20  
  Purchase #6 $238.59   10.629%   $263.9497   $263.95   $263.95   $263.90  
  Purchase #7 $227.87   11.132%   $253.2365   $253.24   $253.25   $253.20  
  7 purchase totals = $869.57       $960.1140   $960.12   $960.15   $960.10