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 $22.99   7.827%   $24.7894   $24.79   $24.80   $24.80  
  Purchase #2 $76.95   8.193%   $83.2545   $83.25   $83.25   $83.30  
  Purchase #3 $57.46   12.362%   $64.5632   $64.56   $64.55   $64.60  
  Purchase #4 $121.55   9.524%   $133.1264   $133.13   $133.15   $133.10  
  Purchase #5 $241.59   5.143%   $254.015   $254.02   $254.00   $254.00  
  Purchase #6 $227.73   5.825%   $240.9953   $241.00   $241.00   $241.00  
  Purchase #7 $72.69   5.184%   $76.4582   $76.46   $76.45   $76.50  
  7 purchase totals = $820.96       $877.2020   $877.21   $877.20   $877.30