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 $17.30   3.356%   $17.8806   $17.88   $17.90   $17.90  
  Purchase #2 $155.75   5.612%   $164.4907   $164.49   $164.50   $164.50  
  Purchase #3 $37.93   6.223%   $40.2904   $40.29   $40.30   $40.30  
  Purchase #4 $223.93   12.589%   $252.1205   $252.12   $252.10   $252.10  
  Purchase #5 $20.30   13.428%   $23.0259   $23.03   $23.05   $23.00  
  Purchase #6 $116.56   10.426%   $128.7125   $128.71   $128.70   $128.70  
  Purchase #7 $238.64   8.364%   $258.5998   $258.60   $258.60   $258.60  
  7 purchase totals = $810.41       $885.1204   $885.12   $885.15   $885.10