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 $201.97   11.127%   $224.4432   $224.44   $224.45   $224.40  
  Purchase #2 $221.36   6.685%   $236.1579   $236.16   $236.15   $236.20  
  Purchase #3 $43.25   8.639%   $46.9864   $46.99   $47.00   $47.00  
  Purchase #4 $120.98   10.636%   $133.8474   $133.85   $133.85   $133.80  
  Purchase #5 $101.69   9.707%   $111.561   $111.56   $111.55   $111.60  
  Purchase #6 $57.55   4.465%   $60.1196   $60.12   $60.10   $60.10  
  Purchase #7 $244.77   7.804%   $263.8719   $263.87   $263.85   $263.90  
  7 purchase totals = $991.57       $1,076.9874   $1,076.99   $1,076.95   $1,077.00