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 $17.49   8.809%   $19.0307   $19.03   $19.05   $19.00  
  Purchase #2 $214.59   12.422%   $241.2464   $241.25   $241.25   $241.20  
  Purchase #3 $16.39   13.116%   $18.5397   $18.54   $18.55   $18.50  
  Purchase #4 $163.51   5.223%   $172.0501   $172.05   $172.05   $172.10  
  Purchase #5 $68.49   9.686%   $75.1239   $75.12   $75.10   $75.10  
  Purchase #6 $74.94   8.287%   $81.1503   $81.15   $81.15   $81.20  
  Purchase #7 $194.89   11.143%   $216.6066   $216.61   $216.60   $216.60  
  7 purchase totals = $750.30       $823.7477   $823.75   $823.75   $823.70