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	$24.33	12.302%	$27.3231	$27.32	$27.30	$27.30
Purchase #2	$166.92	10.706%	$184.7905	$184.79	$184.80	$184.80
Purchase #3	$241.28	11.162%	$268.2117	$268.21	$268.20	$268.20
Purchase #4	$18.29	10.304%	$20.1746	$20.17	$20.15	$20.20
Purchase #5	$68.53	5.725%	$72.4533	$72.45	$72.45	$72.50
Purchase #6	$15.27	13.828%	$17.3815	$17.38	$17.40	$17.40
Purchase #7	$159.44	3.553%	$165.1049	$165.10	$165.10	$165.10
7 purchase totals =	$694.06		$755.4396	$755.42	$755.40	$755.50