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	$243.55	13.191%	$275.6767	$275.68	$275.70	$275.70
Purchase #2	$158.50	5.529%	$167.2635	$167.26	$167.25	$167.30
Purchase #3	$64.82	7.181%	$69.4747	$69.47	$69.45	$69.50
Purchase #4	$58.30	7.700%	$62.7891	$62.79	$62.80	$62.80
Purchase #5	$120.75	6.309%	$128.3681	$128.37	$128.35	$128.40
Purchase #6	$82.50	8.341%	$89.3813	$89.38	$89.40	$89.40
Purchase #7	$190.70	8.330%	$206.5853	$206.59	$206.60	$206.60
7 purchase totals =	$919.12		$999.5387	$999.54	$999.55	$999.70