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	$41.39	6.631%	$44.1346	$44.13	$44.15	$44.10
Purchase #2	$224.61	10.314%	$247.7763	$247.78	$247.80	$247.80
Purchase #3	$238.55	9.256%	$260.6302	$260.63	$260.65	$260.60
Purchase #4	$58.35	10.453%	$64.4493	$64.45	$64.45	$64.40
Purchase #5	$73.58	13.344%	$83.3985	$83.40	$83.40	$83.40
Purchase #6	$223.81	7.606%	$240.833	$240.83	$240.85	$240.80
Purchase #7	$33.94	10.107%	$37.3703	$37.37	$37.35	$37.40
7 purchase totals =	$894.23		$978.5922	$978.59	$978.65	$978.50