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	$191.92	13.668%	$218.1516	$218.15	$218.15	$218.20
Purchase #2	$89.51	8.765%	$97.3556	$97.36	$97.35	$97.40
Purchase #3	$86.92	3.320%	$89.8057	$89.81	$89.80	$89.80
Purchase #4	$154.62	3.688%	$160.3224	$160.32	$160.30	$160.30
Purchase #5	$130.40	4.518%	$136.2915	$136.29	$136.30	$136.30
Purchase #6	$81.48	5.554%	$86.0054	$86.01	$86.00	$86.00
Purchase #7	$9.42	11.105%	$10.4661	$10.47	$10.45	$10.50
7 purchase totals =	$744.27		$798.3983	$798.41	$798.35	$798.50