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 $22.53   5.855%   $23.8491   $23.85   $23.85   $23.80  
  Purchase #2 $191.41   4.361%   $199.7574   $199.76   $199.75   $199.80  
  Purchase #3 $75.55   8.792%   $82.1924   $82.19   $82.20   $82.20  
  Purchase #4 $86.58   4.538%   $90.509   $90.51   $90.50   $90.50  
  Purchase #5 $170.35   3.747%   $176.733   $176.73   $176.75   $176.70  
  Purchase #6 $227.90   3.635%   $236.1842   $236.18   $236.20   $236.20  
  Purchase #7 $21.66   7.613%   $23.309   $23.31   $23.30   $23.30  
  7 purchase totals = $795.98       $832.5341   $832.53   $832.55   $832.50