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	$36.28	7.288%	$38.9241	$38.92	$38.90	$38.90
Purchase #2	$156.94	7.123%	$168.1188	$168.12	$168.10	$168.10
Purchase #3	$151.28	6.764%	$161.5126	$161.51	$161.50	$161.50
Purchase #4	$122.99	13.408%	$139.4805	$139.48	$139.50	$139.50
Purchase #5	$36.92	5.591%	$38.9842	$38.98	$39.00	$39.00
Purchase #6	$114.29	3.726%	$118.5484	$118.55	$118.55	$118.50
Purchase #7	$158.90	6.115%	$168.6167	$168.62	$168.60	$168.60
7 purchase totals =	$777.60		$834.1853	$834.18	$834.15	$834.10