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	$32.52	9.797%	$35.706	$35.71	$35.70	$35.70
Purchase #2	$32.96	13.641%	$37.4561	$37.46	$37.45	$37.50
Purchase #3	$194.72	6.285%	$206.9582	$206.96	$206.95	$207.00
Purchase #4	$92.48	12.215%	$103.7764	$103.78	$103.80	$103.80
Purchase #5	$99.60	13.708%	$113.2532	$113.25	$113.25	$113.30
Purchase #6	$115.45	9.178%	$126.046	$126.05	$126.05	$126.00
Purchase #7	$59.29	3.595%	$61.4215	$61.42	$61.40	$61.40
7 purchase totals =	$627.02		$684.6174	$684.63	$684.60	$684.70