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	$49.56	13.758%	$56.3785	$56.38	$56.40	$56.40
Purchase #2	$42.77	4.319%	$44.6172	$44.62	$44.60	$44.60
Purchase #3	$15.67	10.512%	$17.3172	$17.32	$17.30	$17.30
Purchase #4	$41.42	4.581%	$43.3175	$43.32	$43.30	$43.30
Purchase #5	$45.45	11.679%	$50.7581	$50.76	$50.75	$50.80
Purchase #6	$240.74	9.206%	$262.9025	$262.90	$262.90	$262.90
Purchase #7	$177.88	10.590%	$196.7175	$196.72	$196.70	$196.70
7 purchase totals =	$613.49		$672.0085	$672.02	$671.95	$672.00