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	$116.46	6.358%	$123.8645	$123.86	$123.85	$123.90
Purchase #2	$18.38	12.257%	$20.6328	$20.63	$20.65	$20.60
Purchase #3	$208.71	9.155%	$227.8174	$227.82	$227.80	$227.80
Purchase #4	$138.92	3.356%	$143.5822	$143.58	$143.60	$143.60
Purchase #5	$198.46	12.443%	$223.1544	$223.15	$223.15	$223.20
Purchase #6	$190.58	11.450%	$212.4014	$212.40	$212.40	$212.40
Purchase #7	$38.47	8.590%	$41.7746	$41.77	$41.75	$41.80
7 purchase totals =	$909.98		$993.2273	$993.21	$993.20	$993.30