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	$25.89	11.787%	$28.9417	$28.94	$28.95	$28.90
Purchase #2	$131.87	10.304%	$145.4579	$145.46	$145.45	$145.50
Purchase #3	$55.65	5.554%	$58.7408	$58.74	$58.75	$58.70
Purchase #4	$147.33	3.287%	$152.1727	$152.17	$152.15	$152.20
Purchase #5	$112.77	12.268%	$126.6046	$126.60	$126.60	$126.60
Purchase #6	$6.88	10.796%	$7.6228	$7.62	$7.60	$7.60
Purchase #7	$142.43	7.119%	$152.5696	$152.57	$152.55	$152.60
7 purchase totals =	$622.82		$672.1101	$672.10	$672.05	$672.10