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	$152.53	12.395%	$171.4361	$171.44	$171.45	$171.40
Purchase #2	$70.72	11.411%	$78.7899	$78.79	$78.80	$78.80
Purchase #3	$169.46	11.128%	$188.3175	$188.32	$188.30	$188.30
Purchase #4	$26.95	3.720%	$27.9525	$27.95	$27.95	$28.00
Purchase #5	$102.97	10.195%	$113.4678	$113.47	$113.45	$113.50
Purchase #6	$60.54	3.356%	$62.5717	$62.57	$62.55	$62.60
Purchase #7	$44.28	4.162%	$46.1229	$46.12	$46.10	$46.10
7 purchase totals =	$627.45		$688.6584	$688.66	$688.60	$688.70