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 $243.76   12.517%   $274.2714   $274.27   $274.25   $274.30  
  Purchase #2 $179.85   5.437%   $189.6284   $189.63   $189.65   $189.60  
  Purchase #3 $154.68   9.545%   $169.4442   $169.44   $169.45   $169.40  
  Purchase #4 $111.34   8.351%   $120.638   $120.64   $120.65   $120.60  
  Purchase #5 $38.63   13.647%   $43.9018   $43.90   $43.90   $43.90  
  Purchase #6 $208.91   11.316%   $232.5503   $232.55   $232.55   $232.60  
  Purchase #7 $110.96   12.624%   $124.9676   $124.97   $124.95   $125.00  
  7 purchase totals = $1,048.13       $1,155.4017   $1,155.40   $1,155.40   $1,155.40