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	$49.60	8.166%	$53.6503	$53.65	$53.65	$53.70
Purchase #2	$224.89	10.652%	$248.8453	$248.85	$248.85	$248.80
Purchase #3	$95.74	4.489%	$100.0378	$100.04	$100.05	$100.00
Purchase #4	$75.49	10.722%	$83.584	$83.58	$83.60	$83.60
Purchase #5	$54.95	4.158%	$57.2348	$57.23	$57.25	$57.20
Purchase #6	$219.26	9.585%	$240.2761	$240.28	$240.30	$240.30
Purchase #7	$19.59	3.281%	$20.2327	$20.23	$20.25	$20.20
7 purchase totals =	$739.52		$803.8610	$803.86	$803.95	$803.80