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	$55.88	6.655%	$59.5988	$59.60	$59.60	$59.60
Purchase #2	$143.73	11.153%	$159.7602	$159.76	$159.75	$159.80
Purchase #3	$157.52	9.752%	$172.8814	$172.88	$172.90	$172.90
Purchase #4	$190.59	3.726%	$197.6914	$197.69	$197.70	$197.70
Purchase #5	$57.30	3.331%	$59.2087	$59.21	$59.20	$59.20
Purchase #6	$121.45	9.715%	$133.2489	$133.25	$133.25	$133.20
Purchase #7	$47.60	6.813%	$50.843	$50.84	$50.85	$50.80
7 purchase totals =	$774.07		$833.2324	$833.23	$833.25	$833.20