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	$53.25	3.564%	$55.1478	$55.15	$55.15	$55.10
Purchase #2	$155.70	6.208%	$165.3659	$165.37	$165.35	$165.40
Purchase #3	$245.83	11.766%	$274.7544	$274.75	$274.75	$274.80
Purchase #4	$5.43	9.440%	$5.9426	$5.94	$5.95	$5.90
Purchase #5	$87.83	13.182%	$99.4078	$99.41	$99.40	$99.40
Purchase #6	$175.93	7.170%	$188.5442	$188.54	$188.55	$188.50
Purchase #7	$49.59	3.325%	$51.2389	$51.24	$51.25	$51.20
7 purchase totals =	$773.56		$840.4016	$840.40	$840.40	$840.30