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	$166.89	11.808%	$186.5964	$186.60	$186.60	$186.60
Purchase #2	$169.40	12.477%	$190.536	$190.54	$190.55	$190.50
Purchase #3	$18.44	4.122%	$19.2001	$19.20	$19.20	$19.20
Purchase #4	$93.81	7.542%	$100.8852	$100.89	$100.90	$100.90
Purchase #5	$130.99	10.788%	$145.1212	$145.12	$145.10	$145.10
Purchase #6	$15.78	13.530%	$17.915	$17.92	$17.90	$17.90
Purchase #7	$245.59	7.325%	$263.5795	$263.58	$263.60	$263.60
7 purchase totals =	$840.90		$923.8334	$923.85	$923.85	$923.80