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	$239.56	6.766%	$255.7686	$255.77	$255.75	$255.80
Purchase #2	$161.88	3.640%	$167.7724	$167.77	$167.75	$167.80
Purchase #3	$185.61	10.503%	$205.1046	$205.10	$205.10	$205.10
Purchase #4	$235.25	11.867%	$263.1671	$263.17	$263.15	$263.20
Purchase #5	$173.32	8.555%	$188.1475	$188.15	$188.15	$188.10
Purchase #6	$47.62	12.345%	$53.4987	$53.50	$53.50	$53.50
Purchase #7	$165.89	4.465%	$173.297	$173.30	$173.30	$173.30
7 purchase totals =	$1,209.13		$1,306.7559	$1,306.76	$1,306.70	$1,306.80