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	$230.51	5.700%	$243.6491	$243.65	$243.65	$243.60
Purchase #2	$88.89	8.601%	$96.5354	$96.54	$96.55	$96.50
Purchase #3	$21.72	13.181%	$24.5829	$24.58	$24.60	$24.60
Purchase #4	$15.91	11.658%	$17.7648	$17.76	$17.75	$17.80
Purchase #5	$88.46	4.574%	$92.5062	$92.51	$92.50	$92.50
Purchase #6	$107.74	10.600%	$119.1604	$119.16	$119.15	$119.20
Purchase #7	$179.48	3.200%	$185.2234	$185.22	$185.20	$185.20
7 purchase totals =	$732.71		$779.4222	$779.42	$779.40	$779.40