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	$134.81	12.467%	$151.6168	$151.62	$151.60	$151.60
Purchase #2	$48.38	12.276%	$54.3191	$54.32	$54.30	$54.30
Purchase #3	$118.49	6.688%	$126.4146	$126.41	$126.40	$126.40
Purchase #4	$30.39	10.753%	$33.6578	$33.66	$33.65	$33.70
Purchase #5	$64.79	10.854%	$71.8223	$71.82	$71.80	$71.80
Purchase #6	$136.76	12.423%	$153.7497	$153.75	$153.75	$153.70
Purchase #7	$51.80	5.214%	$54.5009	$54.50	$54.50	$54.50
7 purchase totals =	$585.42		$646.0812	$646.08	$646.00	$646.00