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	$101.88	3.573%	$105.5202	$105.52	$105.50	$105.50
Purchase #2	$117.68	3.653%	$121.9789	$121.98	$122.00	$122.00
Purchase #3	$37.81	3.741%	$39.2245	$39.22	$39.20	$39.20
Purchase #4	$97.83	7.480%	$105.1477	$105.15	$105.15	$105.10
Purchase #5	$152.88	13.563%	$173.6151	$173.62	$173.60	$173.60
Purchase #6	$84.86	6.571%	$90.4362	$90.44	$90.45	$90.40
Purchase #7	$139.63	12.634%	$157.2709	$157.27	$157.25	$157.30
7 purchase totals =	$732.57		$793.1935	$793.20	$793.15	$793.10