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	$154.45	3.287%	$159.5268	$159.53	$159.55	$159.50
Purchase #2	$70.45	12.657%	$79.3669	$79.37	$79.35	$79.40
Purchase #3	$128.94	8.437%	$139.8187	$139.82	$139.80	$139.80
Purchase #4	$80.32	13.757%	$91.3696	$91.37	$91.35	$91.40
Purchase #5	$187.69	4.138%	$195.4566	$195.46	$195.45	$195.50
Purchase #6	$134.59	11.632%	$150.2455	$150.25	$150.25	$150.20
Purchase #7	$33.45	13.126%	$37.8406	$37.84	$37.85	$37.80
7 purchase totals =	$789.89		$853.6247	$853.64	$853.60	$853.60