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 $63.66   12.806%   $71.8123   $71.81   $71.80   $71.80  
  Purchase #2 $25.28   7.409%   $27.153   $27.15   $27.15   $27.20  
  Purchase #3 $89.69   5.849%   $94.936   $94.94   $94.95   $94.90  
  Purchase #4 $83.58   12.455%   $93.9899   $93.99   $94.00   $94.00  
  Purchase #5 $114.61   9.380%   $125.3604   $125.36   $125.35   $125.40  
  Purchase #6 $232.69   4.163%   $242.3769   $242.38   $242.40   $242.40  
  Purchase #7 $214.58   13.177%   $242.8552   $242.86   $242.85   $242.90  
  7 purchase totals = $824.09       $898.4837   $898.49   $898.50   $898.60