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	$92.91	8.162%	$100.4933	$100.49	$100.50	$100.50
Purchase #2	$193.66	10.129%	$213.2758	$213.28	$213.30	$213.30
Purchase #3	$153.91	13.210%	$174.2415	$174.24	$174.25	$174.20
Purchase #4	$61.66	3.686%	$63.9328	$63.93	$63.95	$63.90
Purchase #5	$182.41	7.714%	$196.4811	$196.48	$196.50	$196.50
Purchase #6	$160.78	9.866%	$176.6426	$176.64	$176.65	$176.60
Purchase #7	$243.27	11.488%	$271.2169	$271.22	$271.20	$271.20
7 purchase totals =	$1,088.60		$1,196.2840	$1,196.28	$1,196.35	$1,196.20