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	$139.65	4.810%	$146.3672	$146.37	$146.35	$146.40
Purchase #2	$49.85	7.204%	$53.4412	$53.44	$53.45	$53.40
Purchase #3	$157.94	10.605%	$174.6895	$174.69	$174.70	$174.70
Purchase #4	$18.97	6.176%	$20.1416	$20.14	$20.15	$20.10
Purchase #5	$111.54	7.181%	$119.5497	$119.55	$119.55	$119.50
Purchase #6	$231.50	9.838%	$254.275	$254.28	$254.30	$254.30
Purchase #7	$152.55	11.147%	$169.5547	$169.55	$169.55	$169.60
7 purchase totals =	$862.00		$938.0189	$938.02	$938.05	$938.00