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	$184.32	8.410%	$199.8213	$199.82	$199.80	$199.80
Purchase #2	$122.44	8.284%	$132.5829	$132.58	$132.60	$132.60
Purchase #3	$83.68	9.111%	$91.3041	$91.30	$91.30	$91.30
Purchase #4	$170.74	10.693%	$188.9972	$189.00	$189.00	$189.00
Purchase #5	$94.54	9.830%	$103.8333	$103.83	$103.85	$103.80
Purchase #6	$112.36	13.364%	$127.3758	$127.38	$127.40	$127.40
Purchase #7	$42.29	3.743%	$43.8729	$43.87	$43.85	$43.90
7 purchase totals =	$810.37		$887.7875	$887.78	$887.80	$887.80