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 $246.72   11.648%   $275.4579   $275.46   $275.45   $275.50  
  Purchase #2 $241.69   13.191%   $273.5713   $273.57   $273.55   $273.60  
  Purchase #3 $214.79   9.335%   $234.8406   $234.84   $234.85   $234.80  
  Purchase #4 $188.95   11.372%   $210.4374   $210.44   $210.45   $210.40  
  Purchase #5 $172.33   10.851%   $191.0295   $191.03   $191.05   $191.00  
  Purchase #6 $30.81   13.157%   $34.8637   $34.86   $34.85   $34.90  
  Purchase #7 $236.75   12.394%   $266.0928   $266.09   $266.10   $266.10  
  7 purchase totals = $1,332.04       $1,486.2932   $1,486.29   $1,486.30   $1,486.30