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	$137.82	10.862%	$152.79	$152.79	$152.80	$152.80
Purchase #2	$191.73	10.820%	$212.4752	$212.48	$212.50	$212.50
Purchase #3	$80.29	9.463%	$87.8878	$87.89	$87.90	$87.90
Purchase #4	$39.62	8.853%	$43.1276	$43.13	$43.15	$43.10
Purchase #5	$91.52	5.406%	$96.4676	$96.47	$96.45	$96.50
Purchase #6	$229.51	5.350%	$241.7888	$241.79	$241.80	$241.80
Purchase #7	$157.66	4.755%	$165.1567	$165.16	$165.15	$165.20
7 purchase totals =	$928.15		$999.6937	$999.71	$999.75	$999.80