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	$50.83	11.250%	$56.5484	$56.55	$56.55	$56.50
Purchase #2	$160.78	4.723%	$168.3736	$168.37	$168.35	$168.40
Purchase #3	$128.78	12.525%	$144.9097	$144.91	$144.90	$144.90
Purchase #4	$7.70	9.705%	$8.4473	$8.45	$8.45	$8.40
Purchase #5	$142.55	7.380%	$153.0702	$153.07	$153.05	$153.10
Purchase #6	$30.32	8.224%	$32.8135	$32.81	$32.80	$32.80
Purchase #7	$45.78	10.795%	$50.722	$50.72	$50.70	$50.70
7 purchase totals =	$566.74		$614.8847	$614.88	$614.80	$614.80