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	$145.56	6.398%	$154.8729	$154.87	$154.85	$154.90
Purchase #2	$93.64	13.750%	$106.5155	$106.52	$106.50	$106.50
Purchase #3	$114.30	11.573%	$127.5279	$127.53	$127.55	$127.50
Purchase #4	$43.43	13.485%	$49.2865	$49.29	$49.30	$49.30
Purchase #5	$100.44	10.202%	$110.6869	$110.69	$110.70	$110.70
Purchase #6	$74.72	8.499%	$81.0705	$81.07	$81.05	$81.10
Purchase #7	$123.50	3.681%	$128.046	$128.05	$128.05	$128.00
7 purchase totals =	$695.59		$758.0062	$758.02	$758.00	$758.00