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	$38.56	3.378%	$39.8626	$39.86	$39.85	$39.90
Purchase #2	$22.78	8.702%	$24.7623	$24.76	$24.75	$24.80
Purchase #3	$166.77	13.509%	$189.299	$189.30	$189.30	$189.30
Purchase #4	$51.82	3.478%	$53.6223	$53.62	$53.60	$53.60
Purchase #5	$244.96	9.571%	$268.4051	$268.41	$268.40	$268.40
Purchase #6	$18.53	10.237%	$20.4269	$20.43	$20.45	$20.40
Purchase #7	$54.88	4.655%	$57.4347	$57.43	$57.45	$57.40
7 purchase totals =	$598.30		$653.8129	$653.81	$653.80	$653.80