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 $113.75   4.286%   $118.6253   $118.63   $118.65   $118.60  
  Purchase #2 $156.86   12.265%   $176.0989   $176.10   $176.10   $176.10  
  Purchase #3 $118.71   7.318%   $127.3972   $127.40   $127.40   $127.40  
  Purchase #4 $185.97   4.572%   $194.4725   $194.47   $194.45   $194.50  
  Purchase #5 $93.70   10.423%   $103.4664   $103.47   $103.45   $103.50  
  Purchase #6 $92.25   10.706%   $102.1263   $102.13   $102.15   $102.10  
  Purchase #7 $198.67   13.757%   $226.001   $226.00   $226.00   $226.00  
  7 purchase totals = $959.91       $1,048.1876   $1,048.20   $1,048.20   $1,048.20