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	$147.35	6.317%	$156.6581	$156.66	$156.65	$156.70
Purchase #2	$94.69	11.686%	$105.7555	$105.76	$105.75	$105.80
Purchase #3	$228.64	12.326%	$256.8222	$256.82	$256.80	$256.80
Purchase #4	$241.32	3.112%	$248.8299	$248.83	$248.85	$248.80
Purchase #5	$182.92	4.852%	$191.7953	$191.80	$191.80	$191.80
Purchase #6	$28.64	9.717%	$31.4229	$31.42	$31.40	$31.40
Purchase #7	$151.89	13.268%	$172.0428	$172.04	$172.05	$172.00
7 purchase totals =	$1,075.45		$1,163.3267	$1,163.33	$1,163.30	$1,163.30