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	$53.37	4.593%	$55.8213	$55.82	$55.80	$55.80
Purchase #2	$92.28	4.406%	$96.3459	$96.35	$96.35	$96.30
Purchase #3	$34.61	9.458%	$37.8834	$37.88	$37.90	$37.90
Purchase #4	$68.94	12.105%	$77.2852	$77.29	$77.30	$77.30
Purchase #5	$190.90	12.472%	$214.709	$214.71	$214.70	$214.70
Purchase #6	$131.72	12.741%	$148.5024	$148.50	$148.50	$148.50
Purchase #7	$244.69	13.787%	$278.4254	$278.43	$278.45	$278.40
7 purchase totals =	$816.51		$908.9726	$908.98	$909.00	$908.90