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	$80.25	4.564%	$83.9126	$83.91	$83.90	$83.90
Purchase #2	$116.64	6.450%	$124.1633	$124.16	$124.15	$124.20
Purchase #3	$79.44	5.443%	$83.7639	$83.76	$83.75	$83.80
Purchase #4	$158.42	10.120%	$174.4521	$174.45	$174.45	$174.50
Purchase #5	$130.44	13.698%	$148.3077	$148.31	$148.30	$148.30
Purchase #6	$130.86	7.308%	$140.4232	$140.42	$140.40	$140.40
Purchase #7	$41.55	13.873%	$47.3142	$47.31	$47.30	$47.30
7 purchase totals =	$737.60		$802.3370	$802.32	$802.25	$802.40