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 $98.48   5.798%   $104.1899   $104.19   $104.20   $104.20  
  Purchase #2 $209.61   7.828%   $226.0183   $226.02   $226.00   $226.00  
  Purchase #3 $48.79   6.664%   $52.0414   $52.04   $52.05   $52.00  
  Purchase #4 $45.63   6.570%   $48.6279   $48.63   $48.65   $48.60  
  Purchase #5 $26.94   12.750%   $30.3749   $30.37   $30.35   $30.40  
  Purchase #6 $67.38   8.451%   $73.0743   $73.07   $73.05   $73.10  
  Purchase #7 $177.70   4.134%   $185.0461   $185.05   $185.05   $185.00  
  7 purchase totals = $674.53       $719.3728   $719.37   $719.35   $719.30