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	$151.78	4.323%	$158.3414	$158.34	$158.35	$158.30
Purchase #2	$48.99	11.338%	$54.5445	$54.54	$54.55	$54.50
Purchase #3	$166.37	9.539%	$182.24	$182.24	$182.25	$182.20
Purchase #4	$89.50	10.182%	$98.6129	$98.61	$98.60	$98.60
Purchase #5	$167.40	4.291%	$174.5831	$174.58	$174.60	$174.60
Purchase #6	$181.61	10.586%	$200.8352	$200.84	$200.85	$200.80
Purchase #7	$158.75	8.574%	$172.3612	$172.36	$172.35	$172.40
7 purchase totals =	$964.40		$1,041.5183	$1,041.51	$1,041.55	$1,041.40