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	$165.75	4.606%	$173.3844	$173.38	$173.40	$173.40
Purchase #2	$40.43	13.296%	$45.8056	$45.81	$45.80	$45.80
Purchase #3	$172.72	7.361%	$185.4339	$185.43	$185.45	$185.40
Purchase #4	$245.34	4.113%	$255.4308	$255.43	$255.45	$255.40
Purchase #5	$223.34	4.252%	$232.8364	$232.84	$232.85	$232.80
Purchase #6	$196.33	6.755%	$209.5921	$209.59	$209.60	$209.60
Purchase #7	$128.32	5.362%	$135.2005	$135.20	$135.20	$135.20
7 purchase totals =	$1,172.23		$1,237.6837	$1,237.68	$1,237.75	$1,237.60