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	$70.69	13.308%	$80.0974	$80.10	$80.10	$80.10
Purchase #2	$193.72	3.442%	$200.3878	$200.39	$200.40	$200.40
Purchase #3	$84.95	11.638%	$94.8365	$94.84	$94.85	$94.80
Purchase #4	$176.48	6.614%	$188.1524	$188.15	$188.15	$188.20
Purchase #5	$54.98	13.726%	$62.5266	$62.53	$62.55	$62.50
Purchase #6	$106.30	7.707%	$114.4925	$114.49	$114.50	$114.50
Purchase #7	$143.77	5.659%	$151.9059	$151.91	$151.90	$151.90
7 purchase totals =	$830.89		$892.3991	$892.41	$892.45	$892.40