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	$18.83	7.779%	$20.2948	$20.29	$20.30	$20.30
Purchase #2	$56.36	3.565%	$58.3692	$58.37	$58.35	$58.40
Purchase #3	$217.30	12.204%	$243.8193	$243.82	$243.80	$243.80
Purchase #4	$248.27	12.711%	$279.8276	$279.83	$279.85	$279.80
Purchase #5	$176.81	5.605%	$186.7202	$186.72	$186.70	$186.70
Purchase #6	$120.65	5.231%	$126.9612	$126.96	$126.95	$127.00
Purchase #7	$148.93	11.425%	$165.9453	$165.95	$165.95	$165.90
7 purchase totals =	$987.15		$1,081.9376	$1,081.94	$1,081.90	$1,081.90