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	$17.72	4.134%	$18.4525	$18.45	$18.45	$18.50
Purchase #2	$119.25	6.618%	$127.142	$127.14	$127.15	$127.10
Purchase #3	$57.76	3.867%	$59.9936	$59.99	$60.00	$60.00
Purchase #4	$228.99	11.797%	$256.004	$256.00	$256.00	$256.00
Purchase #5	$154.58	12.187%	$173.4187	$173.42	$173.40	$173.40
Purchase #6	$39.76	6.452%	$42.3253	$42.33	$42.35	$42.30
Purchase #7	$235.37	10.438%	$259.9379	$259.94	$259.95	$259.90
7 purchase totals =	$853.43		$937.2740	$937.27	$937.30	$937.20