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	$113.86	12.695%	$128.3145	$128.31	$128.30	$128.30
Purchase #2	$218.66	7.809%	$235.7352	$235.74	$235.75	$235.70
Purchase #3	$215.43	10.768%	$238.6275	$238.63	$238.65	$238.60
Purchase #4	$16.61	6.175%	$17.6357	$17.64	$17.65	$17.60
Purchase #5	$14.37	10.677%	$15.9043	$15.90	$15.90	$15.90
Purchase #6	$52.70	13.784%	$59.9642	$59.96	$59.95	$60.00
Purchase #7	$56.72	4.677%	$59.3728	$59.37	$59.35	$59.40
7 purchase totals =	$688.35		$755.5542	$755.55	$755.55	$755.50