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	$242.55	11.698%	$270.9235	$270.92	$270.90	$270.90
Purchase #2	$137.65	5.338%	$144.9978	$145.00	$145.00	$145.00
Purchase #3	$146.73	3.747%	$152.228	$152.23	$152.25	$152.20
Purchase #4	$132.25	10.861%	$146.6137	$146.61	$146.60	$146.60
Purchase #5	$169.37	9.104%	$184.7894	$184.79	$184.80	$184.80
Purchase #6	$124.33	13.555%	$141.1829	$141.18	$141.20	$141.20
Purchase #7	$124.87	5.558%	$131.8103	$131.81	$131.80	$131.80
7 purchase totals =	$1,077.75		$1,172.5456	$1,172.54	$1,172.55	$1,172.50