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	$203.70	10.310%	$224.7015	$224.70	$224.70	$224.70
Purchase #2	$54.58	13.427%	$61.9085	$61.91	$61.90	$61.90
Purchase #3	$240.62	9.494%	$263.4645	$263.46	$263.45	$263.50
Purchase #4	$74.77	12.268%	$83.9428	$83.94	$83.95	$83.90
Purchase #5	$132.59	10.788%	$146.8938	$146.89	$146.90	$146.90
Purchase #6	$235.93	9.309%	$257.8927	$257.89	$257.90	$257.90
Purchase #7	$35.87	10.246%	$39.5452	$39.55	$39.55	$39.50
7 purchase totals =	$978.06		$1,078.3490	$1,078.34	$1,078.35	$1,078.30