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	$91.30	13.332%	$103.4721	$103.47	$103.45	$103.50
Purchase #2	$44.71	7.726%	$48.1643	$48.16	$48.15	$48.20
Purchase #3	$19.86	13.469%	$22.5349	$22.53	$22.55	$22.50
Purchase #4	$35.68	7.208%	$38.2518	$38.25	$38.25	$38.30
Purchase #5	$62.65	7.713%	$67.4822	$67.48	$67.50	$67.50
Purchase #6	$233.38	4.818%	$244.6242	$244.62	$244.60	$244.60
Purchase #7	$27.70	13.289%	$31.3811	$31.38	$31.40	$31.40
7 purchase totals =	$515.28		$555.9106	$555.89	$555.90	$556.00