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	$21.31	12.794%	$24.0364	$24.04	$24.05	$24.00
Purchase #2	$156.77	8.615%	$170.2757	$170.28	$170.30	$170.30
Purchase #3	$58.95	7.708%	$63.4939	$63.49	$63.50	$63.50
Purchase #4	$21.93	13.518%	$24.8945	$24.89	$24.90	$24.90
Purchase #5	$95.54	8.325%	$103.4937	$103.49	$103.50	$103.50
Purchase #6	$99.59	10.432%	$109.9792	$109.98	$110.00	$110.00
Purchase #7	$78.80	3.275%	$81.3807	$81.38	$81.40	$81.40
7 purchase totals =	$532.89		$577.5541	$577.55	$577.65	$577.60