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	$230.51	12.434%	$259.1716	$259.17	$259.15	$259.20
Purchase #2	$49.58	4.716%	$51.9182	$51.92	$51.90	$51.90
Purchase #3	$135.68	10.872%	$150.4311	$150.43	$150.45	$150.40
Purchase #4	$22.38	5.576%	$23.6279	$23.63	$23.65	$23.60
Purchase #5	$55.60	10.402%	$61.3835	$61.38	$61.40	$61.40
Purchase #6	$43.31	5.185%	$45.5556	$45.56	$45.55	$45.60
Purchase #7	$32.73	7.114%	$35.0584	$35.06	$35.05	$35.10
7 purchase totals =	$569.79		$627.1463	$627.15	$627.15	$627.20