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	$233.39	13.564%	$265.047	$265.05	$265.05	$265.00
Purchase #2	$133.90	9.240%	$146.2724	$146.27	$146.25	$146.30
Purchase #3	$67.95	4.182%	$70.7917	$70.79	$70.80	$70.80
Purchase #4	$85.91	7.497%	$92.3507	$92.35	$92.35	$92.40
Purchase #5	$18.89	8.697%	$20.5329	$20.53	$20.55	$20.50
Purchase #6	$195.30	4.536%	$204.1588	$204.16	$204.15	$204.20
Purchase #7	$89.57	13.614%	$101.7641	$101.76	$101.75	$101.80
7 purchase totals =	$824.91		$900.9176	$900.91	$900.90	$901.00