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	$141.51	6.814%	$151.1525	$151.15	$151.15	$151.20
Purchase #2	$240.44	12.695%	$270.9639	$270.96	$270.95	$271.00
Purchase #3	$143.28	10.571%	$158.4261	$158.43	$158.45	$158.40
Purchase #4	$219.50	10.529%	$242.6112	$242.61	$242.60	$242.60
Purchase #5	$64.83	13.802%	$73.7778	$73.78	$73.80	$73.80
Purchase #6	$151.85	13.420%	$172.2283	$172.23	$172.25	$172.20
Purchase #7	$120.74	8.710%	$131.2565	$131.26	$131.25	$131.30
7 purchase totals =	$1,082.15		$1,200.4163	$1,200.42	$1,200.45	$1,200.50