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	$115.56	3.387%	$119.474	$119.47	$119.45	$119.50
Purchase #2	$223.45	13.682%	$254.0224	$254.02	$254.00	$254.00
Purchase #3	$144.49	4.775%	$151.3894	$151.39	$151.40	$151.40
Purchase #4	$14.42	6.108%	$15.3008	$15.30	$15.30	$15.30
Purchase #5	$142.60	6.346%	$151.6494	$151.65	$151.65	$151.60
Purchase #6	$79.45	13.808%	$90.4205	$90.42	$90.40	$90.40
Purchase #7	$142.54	10.584%	$157.6264	$157.63	$157.65	$157.60
7 purchase totals =	$862.51		$939.8829	$939.88	$939.85	$939.80