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	$134.58	10.378%	$148.5467	$148.55	$148.55	$148.50
Purchase #2	$81.72	11.306%	$90.9593	$90.96	$90.95	$91.00
Purchase #3	$161.38	11.245%	$179.5272	$179.53	$179.55	$179.50
Purchase #4	$233.44	9.540%	$255.7102	$255.71	$255.70	$255.70
Purchase #5	$53.74	12.350%	$60.3769	$60.38	$60.40	$60.40
Purchase #6	$112.86	12.793%	$127.2982	$127.30	$127.30	$127.30
Purchase #7	$122.41	8.243%	$132.5003	$132.50	$132.50	$132.50
7 purchase totals =	$900.13		$994.9188	$994.93	$994.95	$994.90