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	$166.54	7.182%	$178.5009	$178.50	$178.50	$178.50
Purchase #2	$219.25	9.764%	$240.6576	$240.66	$240.65	$240.70
Purchase #3	$199.89	9.403%	$218.6857	$218.69	$218.70	$218.70
Purchase #4	$22.56	13.558%	$25.6187	$25.62	$25.60	$25.60
Purchase #5	$145.30	10.579%	$160.6713	$160.67	$160.65	$160.70
Purchase #6	$46.83	12.354%	$52.6154	$52.62	$52.60	$52.60
Purchase #7	$124.59	5.186%	$131.0512	$131.05	$131.05	$131.10
7 purchase totals =	$924.96		$1,007.8008	$1,007.81	$1,007.75	$1,007.90