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	$17.67	5.329%	$18.6116	$18.61	$18.60	$18.60
Purchase #2	$154.29	3.367%	$159.4849	$159.48	$159.50	$159.50
Purchase #3	$171.72	12.198%	$192.6664	$192.67	$192.65	$192.70
Purchase #4	$223.43	8.443%	$242.2942	$242.29	$242.30	$242.30
Purchase #5	$166.32	13.116%	$188.1345	$188.13	$188.15	$188.10
Purchase #6	$62.52	7.466%	$67.1877	$67.19	$67.20	$67.20
Purchase #7	$182.79	7.589%	$196.6619	$196.66	$196.65	$196.70
7 purchase totals =	$978.74		$1,065.0412	$1,065.03	$1,065.05	$1,065.10