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	$47.87	12.450%	$53.8298	$53.83	$53.85	$53.80
Purchase #2	$94.89	4.401%	$99.0661	$99.07	$99.05	$99.10
Purchase #3	$145.91	9.212%	$159.3512	$159.35	$159.35	$159.40
Purchase #4	$138.57	6.244%	$147.2223	$147.22	$147.20	$147.20
Purchase #5	$129.42	11.143%	$143.8413	$143.84	$143.85	$143.80
Purchase #6	$31.75	12.126%	$35.6	$35.60	$35.60	$35.60
Purchase #7	$167.82	4.242%	$174.9389	$174.94	$174.95	$174.90
7 purchase totals =	$756.23		$813.8496	$813.85	$813.85	$813.80