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	$37.40	13.627%	$42.4965	$42.50	$42.50	$42.50
Purchase #2	$129.54	7.521%	$139.2827	$139.28	$139.30	$139.30
Purchase #3	$224.38	12.734%	$252.9525	$252.95	$252.95	$253.00
Purchase #4	$163.42	6.498%	$174.039	$174.04	$174.05	$174.00
Purchase #5	$241.58	7.192%	$258.9544	$258.95	$258.95	$259.00
Purchase #6	$47.91	11.860%	$53.5921	$53.59	$53.60	$53.60
Purchase #7	$240.29	7.568%	$258.4751	$258.48	$258.50	$258.50
7 purchase totals =	$1,084.52		$1,179.7923	$1,179.79	$1,179.85	$1,179.90