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	$30.95	8.620%	$33.6179	$33.62	$33.60	$33.60
Purchase #2	$139.59	13.127%	$157.914	$157.91	$157.90	$157.90
Purchase #3	$112.97	9.669%	$123.8931	$123.89	$123.90	$123.90
Purchase #4	$14.57	3.252%	$15.0438	$15.04	$15.05	$15.00
Purchase #5	$195.64	13.330%	$221.7188	$221.72	$221.70	$221.70
Purchase #6	$39.78	5.838%	$42.1024	$42.10	$42.10	$42.10
Purchase #7	$114.77	11.667%	$128.1602	$128.16	$128.15	$128.20
7 purchase totals =	$648.27		$722.4502	$722.44	$722.40	$722.40