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	$25.55	9.842%	$28.0646	$28.06	$28.05	$28.10
Purchase #2	$243.93	4.369%	$254.5873	$254.59	$254.60	$254.60
Purchase #3	$37.49	11.714%	$41.8816	$41.88	$41.90	$41.90
Purchase #4	$91.57	12.282%	$102.8166	$102.82	$102.80	$102.80
Purchase #5	$56.89	7.300%	$61.043	$61.04	$61.05	$61.00
Purchase #6	$241.82	8.849%	$263.2187	$263.22	$263.20	$263.20
Purchase #7	$59.28	5.291%	$62.4165	$62.42	$62.40	$62.40
7 purchase totals =	$756.53		$814.0283	$814.03	$814.00	$814.00