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	$120.50	6.559%	$128.4036	$128.40	$128.40	$128.40
Purchase #2	$55.28	12.213%	$62.0313	$62.03	$62.05	$62.00
Purchase #3	$43.43	6.272%	$46.1539	$46.15	$46.15	$46.20
Purchase #4	$46.72	9.729%	$51.2654	$51.27	$51.25	$51.30
Purchase #5	$241.71	3.457%	$250.0659	$250.07	$250.05	$250.10
Purchase #6	$128.52	12.139%	$144.121	$144.12	$144.10	$144.10
Purchase #7	$12.71	6.336%	$13.5153	$13.52	$13.50	$13.50
7 purchase totals =	$648.87		$695.5564	$695.56	$695.50	$695.60