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	$157.84	4.799%	$165.4147	$165.41	$165.40	$165.40
Purchase #2	$51.77	9.158%	$56.5111	$56.51	$56.50	$56.50
Purchase #3	$43.73	10.502%	$48.3225	$48.32	$48.30	$48.30
Purchase #4	$84.78	5.535%	$89.4726	$89.47	$89.45	$89.50
Purchase #5	$84.72	8.632%	$92.033	$92.03	$92.05	$92.00
Purchase #6	$10.55	4.125%	$10.9852	$10.99	$11.00	$11.00
Purchase #7	$209.27	7.742%	$225.4717	$225.47	$225.45	$225.50
7 purchase totals =	$642.66		$688.2108	$688.20	$688.15	$688.20