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	$108.78	5.696%	$114.9761	$114.98	$115.00	$115.00
Purchase #2	$42.45	7.365%	$45.5764	$45.58	$45.60	$45.60
Purchase #3	$53.44	3.834%	$55.4889	$55.49	$55.50	$55.50
Purchase #4	$82.35	9.489%	$90.1642	$90.16	$90.15	$90.20
Purchase #5	$144.85	5.204%	$152.388	$152.39	$152.40	$152.40
Purchase #6	$100.43	13.703%	$114.1919	$114.19	$114.20	$114.20
Purchase #7	$70.27	5.377%	$74.0484	$74.05	$74.05	$74.00
7 purchase totals =	$602.57		$646.8339	$646.84	$646.90	$646.90