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 $65.32   13.263%   $73.9834   $73.98   $74.00   $74.00  
  Purchase #2 $83.27   11.480%   $92.8294   $92.83   $92.85   $92.80  
  Purchase #3 $207.33   6.733%   $221.2895   $221.29   $221.30   $221.30  
  Purchase #4 $126.30   4.810%   $132.375   $132.38   $132.40   $132.40  
  Purchase #5 $228.30   9.624%   $250.2716   $250.27   $250.25   $250.30  
  Purchase #6 $41.98   6.126%   $44.5517   $44.55   $44.55   $44.60  
  Purchase #7 $232.71   12.138%   $260.9563   $260.96   $260.95   $261.00  
  7 purchase totals = $985.21       $1,076.2569   $1,076.26   $1,076.30   $1,076.40