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	$137.28	6.283%	$145.9053	$145.91	$145.90	$145.90
Purchase #2	$142.79	13.777%	$162.4622	$162.46	$162.45	$162.50
Purchase #3	$147.55	7.164%	$158.1205	$158.12	$158.10	$158.10
Purchase #4	$112.47	6.650%	$119.9493	$119.95	$119.95	$119.90
Purchase #5	$44.49	4.490%	$46.4876	$46.49	$46.50	$46.50
Purchase #6	$47.62	12.585%	$53.613	$53.61	$53.60	$53.60
Purchase #7	$18.40	10.861%	$20.3984	$20.40	$20.40	$20.40
7 purchase totals =	$650.60		$706.9363	$706.94	$706.90	$706.90