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	$158.34	13.234%	$179.2947	$179.29	$179.30	$179.30
Purchase #2	$153.53	9.715%	$168.4454	$168.45	$168.45	$168.40
Purchase #3	$30.49	4.745%	$31.9368	$31.94	$31.95	$31.90
Purchase #4	$45.45	10.121%	$50.05	$50.05	$50.05	$50.10
Purchase #5	$77.33	3.848%	$80.3057	$80.31	$80.30	$80.30
Purchase #6	$143.64	10.838%	$159.2077	$159.21	$159.20	$159.20
Purchase #7	$120.39	6.243%	$127.9059	$127.91	$127.90	$127.90
7 purchase totals =	$729.17		$797.1462	$797.16	$797.15	$797.10