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	$52.45	3.468%	$54.269	$54.27	$54.25	$54.30
Purchase #2	$52.52	12.356%	$59.0094	$59.01	$59.00	$59.00
Purchase #3	$20.90	8.239%	$22.622	$22.62	$22.60	$22.60
Purchase #4	$105.30	6.379%	$112.0171	$112.02	$112.00	$112.00
Purchase #5	$39.38	12.531%	$44.3147	$44.31	$44.30	$44.30
Purchase #6	$18.67	6.195%	$19.8266	$19.83	$19.85	$19.80
Purchase #7	$109.76	11.153%	$122.0015	$122.00	$122.00	$122.00
7 purchase totals =	$398.98		$434.0603	$434.06	$434.00	$434.00