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	$131.58	6.471%	$140.0945	$140.09	$140.10	$140.10
Purchase #2	$30.83	6.687%	$32.8916	$32.89	$32.90	$32.90
Purchase #3	$111.48	7.737%	$120.1052	$120.11	$120.10	$120.10
Purchase #4	$237.88	8.586%	$258.3044	$258.30	$258.30	$258.30
Purchase #5	$49.51	9.320%	$54.1243	$54.12	$54.10	$54.10
Purchase #6	$177.51	12.437%	$199.5869	$199.59	$199.60	$199.60
Purchase #7	$27.29	4.388%	$28.4875	$28.49	$28.50	$28.50
7 purchase totals =	$766.08		$833.5944	$833.59	$833.60	$833.60