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	$78.78	13.659%	$89.5406	$89.54	$89.55	$89.50
Purchase #2	$152.27	4.242%	$158.7293	$158.73	$158.75	$158.70
Purchase #3	$203.42	6.307%	$216.2497	$216.25	$216.25	$216.20
Purchase #4	$199.97	4.606%	$209.1806	$209.18	$209.20	$209.20
Purchase #5	$134.31	3.565%	$139.0982	$139.10	$139.10	$139.10
Purchase #6	$159.56	7.669%	$171.7967	$171.80	$171.80	$171.80
Purchase #7	$47.26	7.522%	$50.8149	$50.81	$50.80	$50.80
7 purchase totals =	$975.57		$1,035.4100	$1,035.41	$1,035.45	$1,035.30