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	$92.86	11.256%	$103.3123	$103.31	$103.30	$103.30
Purchase #2	$19.69	9.345%	$21.53	$21.53	$21.55	$21.50
Purchase #3	$63.57	10.316%	$70.1279	$70.13	$70.15	$70.10
Purchase #4	$30.25	8.778%	$32.9053	$32.91	$32.90	$32.90
Purchase #5	$155.33	7.666%	$167.2376	$167.24	$167.25	$167.20
Purchase #6	$229.67	13.616%	$260.9419	$260.94	$260.95	$260.90
Purchase #7	$152.67	3.773%	$158.4302	$158.43	$158.45	$158.40
7 purchase totals =	$744.04		$814.4852	$814.49	$814.55	$814.30