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	$128.98	12.285%	$144.8252	$144.83	$144.85	$144.80
Purchase #2	$42.33	7.523%	$45.5145	$45.51	$45.50	$45.50
Purchase #3	$53.74	3.454%	$55.5962	$55.60	$55.60	$55.60
Purchase #4	$200.90	13.416%	$227.8527	$227.85	$227.85	$227.90
Purchase #5	$161.38	10.556%	$178.4153	$178.42	$178.40	$178.40
Purchase #6	$204.81	11.312%	$227.9781	$227.98	$228.00	$228.00
Purchase #7	$167.58	8.180%	$181.288	$181.29	$181.30	$181.30
7 purchase totals =	$959.72		$1,061.4700	$1,061.48	$1,061.50	$1,061.50