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	$155.78	6.172%	$165.3947	$165.39	$165.40	$165.40
Purchase #2	$136.59	3.298%	$141.0947	$141.09	$141.10	$141.10
Purchase #3	$85.31	12.120%	$95.6496	$95.65	$95.65	$95.60
Purchase #4	$81.44	10.212%	$89.7567	$89.76	$89.75	$89.80
Purchase #5	$67.51	3.244%	$69.7	$69.70	$69.70	$69.70
Purchase #6	$112.25	3.464%	$116.1383	$116.14	$116.15	$116.10
Purchase #7	$40.69	9.663%	$44.6219	$44.62	$44.60	$44.60
7 purchase totals =	$679.57		$722.3559	$722.35	$722.35	$722.30