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	$74.63	3.498%	$77.2406	$77.24	$77.25	$77.20
Purchase #2	$42.40	7.753%	$45.6873	$45.69	$45.70	$45.70
Purchase #3	$30.50	10.284%	$33.6366	$33.64	$33.65	$33.60
Purchase #4	$10.89	11.197%	$12.1094	$12.11	$12.10	$12.10
Purchase #5	$51.41	9.182%	$56.1305	$56.13	$56.15	$56.10
Purchase #6	$59.35	9.135%	$64.7716	$64.77	$64.75	$64.80
Purchase #7	$199.90	10.566%	$221.0214	$221.02	$221.00	$221.00
7 purchase totals =	$469.08		$510.5974	$510.60	$510.60	$510.50