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	$71.74	12.675%	$80.833	$80.83	$80.85	$80.80
Purchase #2	$73.89	7.705%	$79.5832	$79.58	$79.60	$79.60
Purchase #3	$155.27	11.655%	$173.3667	$173.37	$173.35	$173.40
Purchase #4	$13.50	10.636%	$14.9359	$14.94	$14.95	$14.90
Purchase #5	$218.29	12.195%	$244.9105	$244.91	$244.90	$244.90
Purchase #6	$133.98	7.536%	$144.0767	$144.08	$144.10	$144.10
Purchase #7	$98.82	12.377%	$111.051	$111.05	$111.05	$111.10
7 purchase totals =	$765.49		$848.7570	$848.76	$848.80	$848.80