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	$46.78	13.160%	$52.9362	$52.94	$52.95	$52.90
Purchase #2	$93.31	9.745%	$102.4031	$102.40	$102.40	$102.40
Purchase #3	$199.67	10.563%	$220.7611	$220.76	$220.75	$220.80
Purchase #4	$39.55	7.414%	$42.4822	$42.48	$42.50	$42.50
Purchase #5	$117.54	8.791%	$127.8729	$127.87	$127.85	$127.90
Purchase #6	$191.70	10.860%	$212.5186	$212.52	$212.50	$212.50
Purchase #7	$157.48	9.296%	$172.1193	$172.12	$172.10	$172.10
7 purchase totals =	$846.03		$931.0934	$931.09	$931.05	$931.10