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	$152.47	3.619%	$157.9879	$157.99	$158.00	$158.00
Purchase #2	$66.43	5.845%	$70.3128	$70.31	$70.30	$70.30
Purchase #3	$71.57	13.404%	$81.1632	$81.16	$81.15	$81.20
Purchase #4	$123.66	6.138%	$131.2503	$131.25	$131.25	$131.30
Purchase #5	$39.89	13.798%	$45.394	$45.39	$45.40	$45.40
Purchase #6	$178.47	3.450%	$184.6272	$184.63	$184.65	$184.60
Purchase #7	$241.63	12.514%	$271.8676	$271.87	$271.85	$271.90
7 purchase totals =	$874.12		$942.6030	$942.60	$942.60	$942.70