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	$49.97	10.285%	$55.1094	$55.11	$55.10	$55.10
Purchase #2	$238.54	13.179%	$269.9772	$269.98	$270.00	$270.00
Purchase #3	$79.72	13.130%	$90.1872	$90.19	$90.20	$90.20
Purchase #4	$241.80	12.519%	$272.0709	$272.07	$272.05	$272.10
Purchase #5	$19.80	11.121%	$22.002	$22.00	$22.00	$22.00
Purchase #6	$137.95	4.770%	$144.5302	$144.53	$144.55	$144.50
Purchase #7	$140.53	3.607%	$145.5989	$145.60	$145.60	$145.60
7 purchase totals =	$908.31		$999.4758	$999.48	$999.50	$999.50