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	$11.33	13.565%	$12.8669	$12.87	$12.85	$12.90
Purchase #2	$8.38	4.614%	$8.7667	$8.77	$8.75	$8.80
Purchase #3	$169.53	12.412%	$190.5721	$190.57	$190.55	$190.60
Purchase #4	$185.29	13.787%	$210.8359	$210.84	$210.85	$210.80
Purchase #5	$159.30	8.837%	$173.3773	$173.38	$173.40	$173.40
Purchase #6	$78.93	7.859%	$85.1331	$85.13	$85.15	$85.10
Purchase #7	$148.69	4.128%	$154.8279	$154.83	$154.85	$154.80
7 purchase totals =	$761.45		$836.3799	$836.39	$836.40	$836.40