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	$59.27	8.314%	$64.1977	$64.20	$64.20	$64.20
Purchase #2	$127.69	11.377%	$142.2173	$142.22	$142.20	$142.20
Purchase #3	$22.44	8.740%	$24.4013	$24.40	$24.40	$24.40
Purchase #4	$64.37	10.824%	$71.3374	$71.34	$71.35	$71.30
Purchase #5	$105.87	5.143%	$111.3149	$111.31	$111.30	$111.30
Purchase #6	$67.49	12.827%	$76.1469	$76.15	$76.15	$76.10
Purchase #7	$40.80	10.374%	$45.0326	$45.03	$45.05	$45.00
7 purchase totals =	$487.93		$534.6481	$534.65	$534.65	$534.50