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	$13.94	9.570%	$15.2741	$15.27	$15.25	$15.30
Purchase #2	$129.69	10.564%	$143.3905	$143.39	$143.40	$143.40
Purchase #3	$160.42	7.323%	$172.1676	$172.17	$172.15	$172.20
Purchase #4	$142.40	10.209%	$156.9376	$156.94	$156.95	$156.90
Purchase #5	$148.57	9.241%	$162.2994	$162.30	$162.30	$162.30
Purchase #6	$107.43	3.700%	$111.4049	$111.40	$111.40	$111.40
Purchase #7	$56.88	7.139%	$60.9407	$60.94	$60.95	$60.90
7 purchase totals =	$759.33		$822.4148	$822.41	$822.40	$822.40