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	$96.85	12.861%	$109.3059	$109.31	$109.30	$109.30
Purchase #2	$137.65	5.569%	$145.3157	$145.32	$145.30	$145.30
Purchase #3	$158.98	3.595%	$164.6953	$164.70	$164.70	$164.70
Purchase #4	$93.83	9.577%	$102.8161	$102.82	$102.80	$102.80
Purchase #5	$196.51	12.549%	$221.17	$221.17	$221.15	$221.20
Purchase #6	$202.26	10.499%	$223.4953	$223.50	$223.50	$223.50
Purchase #7	$229.40	11.492%	$255.7626	$255.76	$255.75	$255.80
7 purchase totals =	$1,115.48		$1,222.5609	$1,222.58	$1,222.50	$1,222.60