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	$171.39	4.123%	$178.4564	$178.46	$178.45	$178.50
Purchase #2	$149.40	12.591%	$168.211	$168.21	$168.20	$168.20
Purchase #3	$34.90	10.502%	$38.5652	$38.57	$38.55	$38.60
Purchase #4	$233.68	6.449%	$248.75	$248.75	$248.75	$248.80
Purchase #5	$219.58	3.502%	$227.2697	$227.27	$227.25	$227.30
Purchase #6	$18.91	7.588%	$20.3449	$20.34	$20.35	$20.30
Purchase #7	$131.46	3.499%	$136.0598	$136.06	$136.05	$136.10
7 purchase totals =	$959.32		$1,017.6570	$1,017.66	$1,017.60	$1,017.80