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	$192.28	6.840%	$205.432	$205.43	$205.45	$205.40
Purchase #2	$153.74	12.461%	$172.8975	$172.90	$172.90	$172.90
Purchase #3	$103.69	5.431%	$109.3214	$109.32	$109.30	$109.30
Purchase #4	$65.78	7.231%	$70.5366	$70.54	$70.55	$70.50
Purchase #5	$202.25	10.826%	$224.1456	$224.15	$224.15	$224.10
Purchase #6	$37.54	7.774%	$40.4584	$40.46	$40.45	$40.50
Purchase #7	$159.37	4.165%	$166.0078	$166.01	$166.00	$166.00
7 purchase totals =	$914.65		$988.7993	$988.81	$988.80	$988.70