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	$59.96	13.776%	$68.2201	$68.22	$68.20	$68.20
Purchase #2	$230.55	4.486%	$240.8925	$240.89	$240.90	$240.90
Purchase #3	$90.67	4.736%	$94.9641	$94.96	$94.95	$95.00
Purchase #4	$86.85	4.408%	$90.6783	$90.68	$90.70	$90.70
Purchase #5	$150.26	11.862%	$168.0838	$168.08	$168.10	$168.10
Purchase #6	$123.46	11.353%	$137.4764	$137.48	$137.50	$137.50
Purchase #7	$161.95	11.509%	$180.5888	$180.59	$180.60	$180.60
7 purchase totals =	$903.70		$980.9040	$980.90	$980.95	$981.00