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	$83.82	6.523%	$89.2876	$89.29	$89.30	$89.30
Purchase #2	$53.74	6.303%	$57.1272	$57.13	$57.15	$57.10
Purchase #3	$31.72	11.232%	$35.2828	$35.28	$35.30	$35.30
Purchase #4	$70.96	13.137%	$80.282	$80.28	$80.30	$80.30
Purchase #5	$46.75	8.272%	$50.6172	$50.62	$50.60	$50.60
Purchase #6	$58.67	9.201%	$64.0682	$64.07	$64.05	$64.10
Purchase #7	$233.58	7.162%	$250.309	$250.31	$250.30	$250.30
7 purchase totals =	$579.24		$626.9740	$626.98	$627.00	$627.00