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	$223.72	13.771%	$254.5285	$254.53	$254.55	$254.50
Purchase #2	$100.46	9.439%	$109.9424	$109.94	$109.95	$109.90
Purchase #3	$127.68	9.412%	$139.6972	$139.70	$139.70	$139.70
Purchase #4	$77.34	5.849%	$81.8636	$81.86	$81.85	$81.90
Purchase #5	$54.86	10.486%	$60.6126	$60.61	$60.60	$60.60
Purchase #6	$34.58	11.430%	$38.5325	$38.53	$38.55	$38.50
Purchase #7	$120.56	6.638%	$128.5628	$128.56	$128.55	$128.60
7 purchase totals =	$739.20		$813.7396	$813.73	$813.75	$813.70