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	$42.63	6.565%	$45.4287	$45.43	$45.45	$45.40
Purchase #2	$158.55	13.416%	$179.8211	$179.82	$179.80	$179.80
Purchase #3	$239.65	6.292%	$254.7288	$254.73	$254.75	$254.70
Purchase #4	$11.43	8.503%	$12.4019	$12.40	$12.40	$12.40
Purchase #5	$201.58	9.795%	$221.3248	$221.32	$221.30	$221.30
Purchase #6	$121.76	9.563%	$133.4039	$133.40	$133.40	$133.40
Purchase #7	$84.96	5.110%	$89.3015	$89.30	$89.30	$89.30
7 purchase totals =	$860.56		$936.4107	$936.40	$936.40	$936.30