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	$70.87	3.583%	$73.4093	$73.41	$73.40	$73.40
Purchase #2	$232.46	13.521%	$263.8909	$263.89	$263.90	$263.90
Purchase #3	$36.99	10.481%	$40.8669	$40.87	$40.85	$40.90
Purchase #4	$145.58	9.499%	$159.4086	$159.41	$159.40	$159.40
Purchase #5	$52.40	4.579%	$54.7994	$54.80	$54.80	$54.80
Purchase #6	$34.63	8.323%	$37.5123	$37.51	$37.50	$37.50
Purchase #7	$142.90	7.826%	$154.0834	$154.08	$154.10	$154.10
7 purchase totals =	$715.83		$783.9708	$783.97	$783.95	$784.00