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	$18.59	4.120%	$19.3559	$19.36	$19.35	$19.40
Purchase #2	$100.33	10.122%	$110.4854	$110.49	$110.50	$110.50
Purchase #3	$134.87	11.536%	$150.4286	$150.43	$150.45	$150.40
Purchase #4	$83.50	6.629%	$89.0352	$89.04	$89.05	$89.00
Purchase #5	$48.25	8.311%	$52.2601	$52.26	$52.25	$52.30
Purchase #6	$114.73	11.252%	$127.6394	$127.64	$127.65	$127.60
Purchase #7	$70.76	7.618%	$76.1505	$76.15	$76.15	$76.20
7 purchase totals =	$571.03		$625.3551	$625.37	$625.40	$625.40