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	$89.81	11.354%	$100.007	$100.01	$100.00	$100.00
Purchase #2	$83.72	3.615%	$86.7465	$86.75	$86.75	$86.70
Purchase #3	$10.34	4.380%	$10.7929	$10.79	$10.80	$10.80
Purchase #4	$162.51	6.681%	$173.3673	$173.37	$173.35	$173.40
Purchase #5	$164.88	3.615%	$170.8404	$170.84	$170.85	$170.80
Purchase #6	$182.65	4.471%	$190.8163	$190.82	$190.80	$190.80
Purchase #7	$177.79	4.256%	$185.3567	$185.36	$185.35	$185.40
7 purchase totals =	$871.70		$917.9271	$917.94	$917.90	$917.90