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	$247.34	3.188%	$255.2252	$255.23	$255.25	$255.20
Purchase #2	$114.80	11.346%	$127.8252	$127.83	$127.85	$127.80
Purchase #3	$150.27	13.369%	$170.3596	$170.36	$170.35	$170.40
Purchase #4	$30.47	3.641%	$31.5794	$31.58	$31.60	$31.60
Purchase #5	$191.64	7.706%	$206.4078	$206.41	$206.40	$206.40
Purchase #6	$226.77	12.367%	$254.8146	$254.81	$254.80	$254.80
Purchase #7	$231.60	4.653%	$242.3763	$242.38	$242.40	$242.40
7 purchase totals =	$1,192.89		$1,288.5881	$1,288.60	$1,288.65	$1,288.60