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	$19.46	6.538%	$20.7323	$20.73	$20.75	$20.70
Purchase #2	$25.98	6.429%	$27.6503	$27.65	$27.65	$27.70
Purchase #3	$66.36	4.530%	$69.3661	$69.37	$69.35	$69.40
Purchase #4	$14.91	3.124%	$15.3758	$15.38	$15.40	$15.40
Purchase #5	$146.57	5.679%	$154.8937	$154.89	$154.90	$154.90
Purchase #6	$48.92	11.411%	$54.5023	$54.50	$54.50	$54.50
Purchase #7	$61.52	6.251%	$65.3656	$65.37	$65.35	$65.40
7 purchase totals =	$383.72		$407.8861	$407.89	$407.90	$408.00