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 $41.55   5.569%   $43.8639   $43.86   $43.85   $43.90  
  Purchase #2 $208.26   10.396%   $229.9107   $229.91   $229.90   $229.90  
  Purchase #3 $229.65   13.697%   $261.1052   $261.11   $261.10   $261.10  
  Purchase #4 $95.44   8.737%   $103.7786   $103.78   $103.80   $103.80  
  Purchase #5 $140.27   6.371%   $149.2066   $149.21   $149.20   $149.20  
  Purchase #6 $107.65   10.547%   $119.0038   $119.00   $119.00   $119.00  
  Purchase #7 $160.45   4.316%   $167.375   $167.38   $167.40   $167.40  
  7 purchase totals = $983.27       $1,074.2438   $1,074.25   $1,074.25   $1,074.30