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	$68.37	10.361%	$75.4538	$75.45	$75.45	$75.50
Purchase #2	$166.31	4.692%	$174.1133	$174.11	$174.10	$174.10
Purchase #3	$48.73	8.353%	$52.8004	$52.80	$52.80	$52.80
Purchase #4	$177.64	12.648%	$200.1079	$200.11	$200.10	$200.10
Purchase #5	$28.97	13.276%	$32.8161	$32.82	$32.80	$32.80
Purchase #6	$74.59	4.685%	$78.0845	$78.08	$78.10	$78.10
Purchase #7	$143.60	11.431%	$160.0149	$160.01	$160.00	$160.00
7 purchase totals =	$708.21		$773.3909	$773.38	$773.35	$773.40