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	$183.31	3.323%	$189.4014	$189.40	$189.40	$189.40
Purchase #2	$18.62	8.795%	$20.2576	$20.26	$20.25	$20.30
Purchase #3	$99.32	4.326%	$103.6166	$103.62	$103.60	$103.60
Purchase #4	$111.33	11.455%	$124.0829	$124.08	$124.10	$124.10
Purchase #5	$241.71	6.731%	$257.9795	$257.98	$258.00	$258.00
Purchase #6	$42.30	7.172%	$45.3338	$45.33	$45.35	$45.30
Purchase #7	$227.98	13.778%	$259.3911	$259.39	$259.40	$259.40
7 purchase totals =	$924.57		$1,000.0629	$1,000.06	$1,000.10	$1,000.10