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 $22.75   4.311%   $23.7308   $23.73   $23.75   $23.70  
  Purchase #2 $240.67   8.566%   $261.2858   $261.29   $261.30   $261.30  
  Purchase #3 $161.89   9.426%   $177.1498   $177.15   $177.15   $177.10  
  Purchase #4 $191.79   13.556%   $217.7891   $217.79   $217.80   $217.80  
  Purchase #5 $73.88   11.821%   $82.6134   $82.61   $82.60   $82.60  
  Purchase #6 $192.74   4.780%   $201.953   $201.95   $201.95   $202.00  
  Purchase #7 $52.89   13.769%   $60.1724   $60.17   $60.15   $60.20  
  7 purchase totals = $936.61       $1,024.6943   $1,024.69   $1,024.70   $1,024.70