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	$81.89	4.727%	$85.7609	$85.76	$85.75	$85.80
Purchase #2	$43.74	10.129%	$48.1704	$48.17	$48.15	$48.20
Purchase #3	$213.38	12.759%	$240.6052	$240.61	$240.60	$240.60
Purchase #4	$140.32	12.723%	$158.1729	$158.17	$158.15	$158.20
Purchase #5	$67.44	4.194%	$70.2684	$70.27	$70.25	$70.30
Purchase #6	$91.48	9.296%	$99.984	$99.98	$100.00	$100.00
Purchase #7	$55.52	10.816%	$61.525	$61.53	$61.55	$61.50
7 purchase totals =	$693.77		$764.4868	$764.49	$764.45	$764.60