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	$190.58	11.322%	$212.1575	$212.16	$212.15	$212.20
Purchase #2	$100.90	3.492%	$104.4234	$104.42	$104.40	$104.40
Purchase #3	$234.81	13.297%	$266.0327	$266.03	$266.05	$266.00
Purchase #4	$250.50	5.504%	$264.2875	$264.29	$264.30	$264.30
Purchase #5	$90.58	3.663%	$93.8979	$93.90	$93.90	$93.90
Purchase #6	$18.50	10.494%	$20.4414	$20.44	$20.45	$20.40
Purchase #7	$73.77	6.587%	$78.6292	$78.63	$78.65	$78.60
7 purchase totals =	$959.64		$1,039.8696	$1,039.87	$1,039.90	$1,039.80