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	$239.69	3.465%	$247.9953	$248.00	$248.00	$248.00
Purchase #2	$41.28	10.544%	$45.6326	$45.63	$45.65	$45.60
Purchase #3	$91.35	12.131%	$102.4317	$102.43	$102.45	$102.40
Purchase #4	$227.69	9.135%	$248.4895	$248.49	$248.50	$248.50
Purchase #5	$55.69	10.313%	$61.4333	$61.43	$61.45	$61.40
Purchase #6	$227.26	12.565%	$255.8152	$255.82	$255.80	$255.80
Purchase #7	$33.26	13.120%	$37.6237	$37.62	$37.60	$37.60
7 purchase totals =	$916.22		$999.4213	$999.42	$999.45	$999.30