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	$37.34	7.577%	$40.1693	$40.17	$40.15	$40.20
Purchase #2	$47.79	13.700%	$54.3372	$54.34	$54.35	$54.30
Purchase #3	$83.45	8.781%	$90.7777	$90.78	$90.80	$90.80
Purchase #4	$249.79	6.734%	$266.6109	$266.61	$266.60	$266.60
Purchase #5	$35.32	9.325%	$38.6136	$38.61	$38.60	$38.60
Purchase #6	$26.40	13.740%	$30.0274	$30.03	$30.05	$30.00
Purchase #7	$232.45	11.309%	$258.7378	$258.74	$258.75	$258.70
7 purchase totals =	$712.54		$779.2739	$779.28	$779.30	$779.20