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	$26.25	7.707%	$28.2731	$28.27	$28.25	$28.30
Purchase #2	$158.46	12.560%	$178.3626	$178.36	$178.35	$178.40
Purchase #3	$140.29	13.271%	$158.9079	$158.91	$158.90	$158.90
Purchase #4	$25.49	10.212%	$28.093	$28.09	$28.10	$28.10
Purchase #5	$168.78	11.768%	$188.642	$188.64	$188.65	$188.60
Purchase #6	$130.60	9.194%	$142.6074	$142.61	$142.60	$142.60
Purchase #7	$53.94	13.167%	$61.0423	$61.04	$61.05	$61.00
7 purchase totals =	$703.81		$785.9283	$785.92	$785.90	$785.90