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	$91.38	12.159%	$102.4909	$102.49	$102.50	$102.50
Purchase #2	$187.66	12.305%	$210.7516	$210.75	$210.75	$210.80
Purchase #3	$11.33	9.568%	$12.4141	$12.41	$12.40	$12.40
Purchase #4	$43.26	6.714%	$46.1645	$46.16	$46.15	$46.20
Purchase #5	$52.99	12.494%	$59.6106	$59.61	$59.60	$59.60
Purchase #6	$18.52	4.769%	$19.4032	$19.40	$19.40	$19.40
Purchase #7	$101.35	4.306%	$105.7141	$105.71	$105.70	$105.70
7 purchase totals =	$506.49		$556.5490	$556.53	$556.50	$556.60