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	$18.93	9.436%	$20.7162	$20.72	$20.70	$20.70
Purchase #2	$42.31	7.413%	$45.4464	$45.45	$45.45	$45.40
Purchase #3	$150.39	5.525%	$158.699	$158.70	$158.70	$158.70
Purchase #4	$181.69	10.339%	$200.4749	$200.47	$200.45	$200.50
Purchase #5	$75.61	4.119%	$78.7244	$78.72	$78.70	$78.70
Purchase #6	$165.71	3.410%	$171.3607	$171.36	$171.35	$171.40
Purchase #7	$207.53	4.208%	$216.2629	$216.26	$216.25	$216.30
7 purchase totals =	$842.17		$891.6845	$891.68	$891.60	$891.70