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	$237.67	7.356%	$255.153	$255.15	$255.15	$255.20
Purchase #2	$240.28	6.483%	$255.8574	$255.86	$255.85	$255.90
Purchase #3	$157.44	6.379%	$167.4831	$167.48	$167.50	$167.50
Purchase #4	$113.29	9.543%	$124.1013	$124.10	$124.10	$124.10
Purchase #5	$45.40	9.634%	$49.7738	$49.77	$49.75	$49.80
Purchase #6	$91.78	12.599%	$103.3434	$103.34	$103.35	$103.30
Purchase #7	$127.43	6.754%	$136.0366	$136.04	$136.05	$136.00
7 purchase totals =	$1,013.29		$1,091.7486	$1,091.74	$1,091.75	$1,091.80