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	$152.79	4.846%	$160.1942	$160.19	$160.20	$160.20
Purchase #2	$115.61	13.108%	$130.7642	$130.76	$130.75	$130.80
Purchase #3	$109.92	12.541%	$123.7051	$123.71	$123.70	$123.70
Purchase #4	$58.65	11.340%	$65.3009	$65.30	$65.30	$65.30
Purchase #5	$52.94	3.546%	$54.8173	$54.82	$54.80	$54.80
Purchase #6	$53.48	13.705%	$60.8094	$60.81	$60.80	$60.80
Purchase #7	$47.84	13.770%	$54.4276	$54.43	$54.45	$54.40
7 purchase totals =	$591.23		$650.0187	$650.02	$650.00	$650.00