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	$39.67	9.103%	$43.2812	$43.28	$43.30	$43.30
Purchase #2	$223.77	6.526%	$238.3732	$238.37	$238.35	$238.40
Purchase #3	$90.63	10.569%	$100.2087	$100.21	$100.20	$100.20
Purchase #4	$139.82	12.760%	$157.661	$157.66	$157.65	$157.70
Purchase #5	$6.66	3.222%	$6.8746	$6.87	$6.85	$6.90
Purchase #6	$59.99	4.136%	$62.4712	$62.47	$62.45	$62.50
Purchase #7	$92.29	13.605%	$104.8461	$104.85	$104.85	$104.80
7 purchase totals =	$652.83		$713.7160	$713.71	$713.65	$713.80