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	$25.48	11.872%	$28.505	$28.51	$28.50	$28.50
Purchase #2	$189.33	3.874%	$196.6646	$196.66	$196.65	$196.70
Purchase #3	$116.43	9.155%	$127.0892	$127.09	$127.10	$127.10
Purchase #4	$70.72	12.534%	$79.584	$79.58	$79.60	$79.60
Purchase #5	$139.53	6.545%	$148.6622	$148.66	$148.65	$148.70
Purchase #6	$18.34	13.445%	$20.8058	$20.81	$20.80	$20.80
Purchase #7	$126.95	3.167%	$130.9705	$130.97	$130.95	$131.00
7 purchase totals =	$686.78		$732.2813	$732.28	$732.25	$732.40