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	$52.85	6.674%	$56.3772	$56.38	$56.40	$56.40
Purchase #2	$10.51	7.723%	$11.3217	$11.32	$11.30	$11.30
Purchase #3	$184.71	3.781%	$191.6939	$191.69	$191.70	$191.70
Purchase #4	$97.69	13.619%	$110.9944	$110.99	$111.00	$111.00
Purchase #5	$94.26	10.403%	$104.0659	$104.07	$104.05	$104.10
Purchase #6	$125.55	4.672%	$131.4157	$131.42	$131.40	$131.40
Purchase #7	$240.57	4.109%	$250.455	$250.46	$250.45	$250.50
7 purchase totals =	$806.14		$856.3238	$856.33	$856.30	$856.40