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 $23.78   8.338%   $25.7628   $25.76   $25.75   $25.80  
  Purchase #2 $214.47   7.656%   $230.8898   $230.89   $230.90   $230.90  
  Purchase #3 $84.76   8.441%   $91.9146   $91.91   $91.90   $91.90  
  Purchase #4 $28.39   6.484%   $30.2308   $30.23   $30.25   $30.20  
  Purchase #5 $14.78   4.490%   $15.4436   $15.44   $15.45   $15.40  
  Purchase #6 $165.43   10.162%   $182.241   $182.24   $182.25   $182.20  
  Purchase #7 $223.84   8.314%   $242.4501   $242.45   $242.45   $242.50  
  7 purchase totals = $755.45       $818.9327   $818.92   $818.95   $818.90