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 $192.39   4.716%   $201.4631   $201.46   $201.45   $201.50  
  Purchase #2 $124.42   5.249%   $130.9508   $130.95   $130.95   $131.00  
  Purchase #3 $21.64   12.275%   $24.2963   $24.30   $24.30   $24.30  
  Purchase #4 $228.84   7.226%   $245.376   $245.38   $245.40   $245.40  
  Purchase #5 $226.58   12.553%   $255.0226   $255.02   $255.00   $255.00  
  Purchase #6 $248.50   4.693%   $260.1621   $260.16   $260.15   $260.20  
  Purchase #7 $29.43   9.238%   $32.1487   $32.15   $32.15   $32.10  
  7 purchase totals = $1,071.80       $1,149.4196   $1,149.42   $1,149.40   $1,149.50