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	$128.72	12.565%	$144.8937	$144.89	$144.90	$144.90
Purchase #2	$42.46	6.725%	$45.3154	$45.32	$45.30	$45.30
Purchase #3	$5.69	3.825%	$5.9076	$5.91	$5.90	$5.90
Purchase #4	$68.99	10.384%	$76.1539	$76.15	$76.15	$76.20
Purchase #5	$212.85	13.353%	$241.2719	$241.27	$241.25	$241.30
Purchase #6	$129.33	11.574%	$144.2987	$144.30	$144.30	$144.30
Purchase #7	$20.93	10.140%	$23.0523	$23.05	$23.05	$23.10
7 purchase totals =	$608.97		$680.8935	$680.89	$680.85	$681.00