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	$107.30	4.171%	$111.7755	$111.78	$111.80	$111.80
Purchase #2	$198.36	10.118%	$218.4301	$218.43	$218.45	$218.40
Purchase #3	$108.94	10.274%	$120.1325	$120.13	$120.15	$120.10
Purchase #4	$10.88	8.610%	$11.8168	$11.82	$11.80	$11.80
Purchase #5	$231.94	3.730%	$240.5914	$240.59	$240.60	$240.60
Purchase #6	$168.47	13.518%	$191.2438	$191.24	$191.25	$191.20
Purchase #7	$9.65	8.659%	$10.4856	$10.49	$10.50	$10.50
7 purchase totals =	$835.54		$904.4757	$904.48	$904.55	$904.40