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	$104.30	4.102%	$108.5784	$108.58	$108.60	$108.60
Purchase #2	$89.36	8.590%	$97.036	$97.04	$97.05	$97.00
Purchase #3	$224.28	13.396%	$254.3245	$254.32	$254.30	$254.30
Purchase #4	$196.34	4.279%	$204.7414	$204.74	$204.75	$204.70
Purchase #5	$93.26	13.130%	$105.505	$105.51	$105.50	$105.50
Purchase #6	$25.70	11.386%	$28.6262	$28.63	$28.65	$28.60
Purchase #7	$37.62	13.142%	$42.564	$42.56	$42.55	$42.60
7 purchase totals =	$770.86		$841.3755	$841.38	$841.40	$841.30