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	$36.99	3.839%	$38.41	$38.41	$38.40	$38.40
Purchase #2	$66.62	7.785%	$71.8064	$71.81	$71.80	$71.80
Purchase #3	$158.38	9.124%	$172.8306	$172.83	$172.85	$172.80
Purchase #4	$244.95	7.120%	$262.3904	$262.39	$262.40	$262.40
Purchase #5	$76.70	9.642%	$84.0954	$84.10	$84.10	$84.10
Purchase #6	$180.52	11.308%	$200.9332	$200.93	$200.95	$200.90
Purchase #7	$61.31	10.556%	$67.7819	$67.78	$67.80	$67.80
7 purchase totals =	$825.47		$898.2479	$898.25	$898.30	$898.20