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	$101.97	6.849%	$108.9539	$108.95	$108.95	$109.00
Purchase #2	$96.36	8.397%	$104.4513	$104.45	$104.45	$104.50
Purchase #3	$57.52	6.135%	$61.0489	$61.05	$61.05	$61.00
Purchase #4	$172.78	6.501%	$184.0124	$184.01	$184.00	$184.00
Purchase #5	$95.92	9.823%	$105.3422	$105.34	$105.35	$105.30
Purchase #6	$35.59	6.284%	$37.8265	$37.83	$37.85	$37.80
Purchase #7	$43.59	7.244%	$46.7477	$46.75	$46.75	$46.70
7 purchase totals =	$603.73		$648.3829	$648.38	$648.40	$648.30