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	$67.31	12.115%	$75.4646	$75.46	$75.45	$75.50
Purchase #2	$127.39	5.398%	$134.2665	$134.27	$134.25	$134.30
Purchase #3	$80.55	10.862%	$89.2993	$89.30	$89.30	$89.30
Purchase #4	$187.94	9.236%	$205.2981	$205.30	$205.30	$205.30
Purchase #5	$122.43	4.213%	$127.588	$127.59	$127.60	$127.60
Purchase #6	$107.75	8.371%	$116.7698	$116.77	$116.75	$116.80
Purchase #7	$185.76	9.773%	$203.9143	$203.91	$203.90	$203.90
7 purchase totals =	$879.13		$952.6006	$952.60	$952.55	$952.70