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 $200.58   11.556%   $223.759   $223.76   $223.75   $223.80  
  Purchase #2 $5.63   10.545%   $6.2237   $6.22   $6.20   $6.20  
  Purchase #3 $95.66   12.807%   $107.9112   $107.91   $107.90   $107.90  
  Purchase #4 $92.65   5.484%   $97.7309   $97.73   $97.75   $97.70  
  Purchase #5 $62.39   8.852%   $67.9128   $67.91   $67.90   $67.90  
  Purchase #6 $126.68   11.205%   $140.8745   $140.87   $140.85   $140.90  
  Purchase #7 $142.58   5.484%   $150.3991   $150.40   $150.40   $150.40  
  7 purchase totals = $726.17       $794.8112   $794.80   $794.75   $794.80