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	$60.34	13.230%	$68.323	$68.32	$68.30	$68.30
Purchase #2	$105.88	3.410%	$109.4905	$109.49	$109.50	$109.50
Purchase #3	$143.68	4.795%	$150.5695	$150.57	$150.55	$150.60
Purchase #4	$30.87	9.670%	$33.8551	$33.86	$33.85	$33.90
Purchase #5	$40.54	5.126%	$42.6181	$42.62	$42.60	$42.60
Purchase #6	$133.60	12.823%	$150.7315	$150.73	$150.75	$150.70
Purchase #7	$55.35	6.353%	$58.8664	$58.87	$58.85	$58.90
7 purchase totals =	$570.26		$614.4541	$614.46	$614.40	$614.50