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	$212.91	4.767%	$223.0594	$223.06	$223.05	$223.10
Purchase #2	$55.78	11.363%	$62.1183	$62.12	$62.10	$62.10
Purchase #3	$129.52	11.451%	$144.3513	$144.35	$144.35	$144.40
Purchase #4	$40.55	3.769%	$42.0783	$42.08	$42.10	$42.10
Purchase #5	$18.53	9.204%	$20.2355	$20.24	$20.25	$20.20
Purchase #6	$37.51	7.752%	$40.4178	$40.42	$40.40	$40.40
Purchase #7	$108.92	7.157%	$116.7154	$116.72	$116.70	$116.70
7 purchase totals =	$603.72		$648.9760	$648.99	$648.95	$649.00