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	$68.62	12.469%	$77.1762	$77.18	$77.20	$77.20
Purchase #2	$76.89	8.626%	$83.5225	$83.52	$83.50	$83.50
Purchase #3	$141.61	8.472%	$153.6072	$153.61	$153.60	$153.60
Purchase #4	$169.88	10.754%	$188.1489	$188.15	$188.15	$188.10
Purchase #5	$64.81	13.507%	$73.5639	$73.56	$73.55	$73.60
Purchase #6	$218.97	10.186%	$241.2743	$241.27	$241.25	$241.30
Purchase #7	$235.44	8.323%	$255.0357	$255.04	$255.05	$255.00
7 purchase totals =	$976.22		$1,072.3287	$1,072.33	$1,072.30	$1,072.30