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	$93.70	12.683%	$105.584	$105.58	$105.60	$105.60
Purchase #2	$19.48	4.550%	$20.3663	$20.37	$20.35	$20.40
Purchase #3	$147.88	7.112%	$158.3972	$158.40	$158.40	$158.40
Purchase #4	$190.80	8.314%	$206.6631	$206.66	$206.65	$206.70
Purchase #5	$206.43	8.359%	$223.6855	$223.69	$223.70	$223.70
Purchase #6	$65.71	13.349%	$74.4816	$74.48	$74.50	$74.50
Purchase #7	$83.50	7.208%	$89.5187	$89.52	$89.50	$89.50
7 purchase totals =	$807.50		$878.6964	$878.70	$878.70	$878.80