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	$9.99	4.236%	$10.4132	$10.41	$10.40	$10.40
Purchase #2	$39.54	7.406%	$42.4683	$42.47	$42.45	$42.50
Purchase #3	$41.72	9.207%	$45.5612	$45.56	$45.55	$45.60
Purchase #4	$76.63	9.488%	$83.9007	$83.90	$83.90	$83.90
Purchase #5	$55.72	8.669%	$60.5504	$60.55	$60.55	$60.60
Purchase #6	$178.62	6.464%	$190.166	$190.17	$190.15	$190.20
Purchase #7	$9.86	7.547%	$10.6041	$10.60	$10.60	$10.60
7 purchase totals =	$412.08		$443.6639	$443.66	$443.60	$443.80