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 $58.44   13.805%   $66.5076   $66.51   $66.50   $66.50  
  Purchase #2 $130.73   9.268%   $142.8461   $142.85   $142.85   $142.80  
  Purchase #3 $6.98   4.269%   $7.278   $7.28   $7.30   $7.30  
  Purchase #4 $47.50   4.460%   $49.6185   $49.62   $49.60   $49.60  
  Purchase #5 $124.57   12.475%   $140.1101   $140.11   $140.10   $140.10  
  Purchase #6 $200.31   4.276%   $208.8753   $208.88   $208.90   $208.90  
  Purchase #7 $60.99   4.367%   $63.6534   $63.65   $63.65   $63.70  
  7 purchase totals = $629.52       $678.8890   $678.90   $678.90   $678.90