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	$175.49	8.612%	$190.6032	$190.60	$190.60	$190.60
Purchase #2	$38.42	13.225%	$43.501	$43.50	$43.50	$43.50
Purchase #3	$114.38	9.500%	$125.2461	$125.25	$125.25	$125.20
Purchase #4	$22.84	4.492%	$23.866	$23.87	$23.85	$23.90
Purchase #5	$91.72	8.786%	$99.7785	$99.78	$99.80	$99.80
Purchase #6	$238.71	5.860%	$252.6984	$252.70	$252.70	$252.70
Purchase #7	$85.90	3.818%	$89.1797	$89.18	$89.20	$89.20
7 purchase totals =	$767.46		$824.8729	$824.88	$824.90	$824.90