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	$243.92	9.678%	$267.5266	$267.53	$267.55	$267.50
Purchase #2	$137.89	5.366%	$145.2892	$145.29	$145.30	$145.30
Purchase #3	$159.63	12.297%	$179.2597	$179.26	$179.25	$179.30
Purchase #4	$100.67	10.865%	$111.6078	$111.61	$111.60	$111.60
Purchase #5	$40.67	10.747%	$45.0408	$45.04	$45.05	$45.00
Purchase #6	$75.86	7.318%	$81.4114	$81.41	$81.40	$81.40
Purchase #7	$14.45	4.607%	$15.1157	$15.12	$15.10	$15.10
7 purchase totals =	$773.09		$845.2512	$845.26	$845.25	$845.20