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 $245.94   11.601%   $274.4715   $274.47   $274.45   $274.50  
  Purchase #2 $73.84   3.212%   $76.2117   $76.21   $76.20   $76.20  
  Purchase #3 $80.93   13.738%   $92.0482   $92.05   $92.05   $92.00  
  Purchase #4 $95.63   12.212%   $107.3083   $107.31   $107.30   $107.30  
  Purchase #5 $13.88   4.503%   $14.505   $14.51   $14.50   $14.50  
  Purchase #6 $156.61   6.800%   $167.2595   $167.26   $167.25   $167.30  
  Purchase #7 $216.97   8.522%   $235.4602   $235.46   $235.45   $235.50  
  7 purchase totals = $883.80       $967.2644   $967.27   $967.20   $967.30