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	$87.42	13.670%	$99.3703	$99.37	$99.35	$99.40
Purchase #2	$179.87	9.115%	$196.2652	$196.27	$196.25	$196.30
Purchase #3	$48.28	11.157%	$53.6666	$53.67	$53.65	$53.70
Purchase #4	$27.33	3.842%	$28.38	$28.38	$28.40	$28.40
Purchase #5	$25.77	11.541%	$28.7441	$28.74	$28.75	$28.70
Purchase #6	$102.63	10.480%	$113.3856	$113.39	$113.40	$113.40
Purchase #7	$59.50	7.795%	$64.138	$64.14	$64.15	$64.10
7 purchase totals =	$530.80		$583.9498	$583.96	$583.95	$584.00