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	$137.39	6.577%	$146.4261	$146.43	$146.45	$146.40
Purchase #2	$26.26	10.415%	$28.995	$29.00	$29.00	$29.00
Purchase #3	$213.91	12.379%	$240.3899	$240.39	$240.40	$240.40
Purchase #4	$219.43	13.792%	$249.6938	$249.69	$249.70	$249.70
Purchase #5	$111.70	13.820%	$127.1369	$127.14	$127.15	$127.10
Purchase #6	$135.52	11.822%	$151.5412	$151.54	$151.55	$151.50
Purchase #7	$23.80	5.519%	$25.1135	$25.11	$25.10	$25.10
7 purchase totals =	$868.01		$969.2964	$969.30	$969.35	$969.20