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	$26.37	4.606%	$27.5846	$27.58	$27.60	$27.60
Purchase #2	$134.34	9.368%	$146.925	$146.93	$146.95	$146.90
Purchase #3	$112.72	9.469%	$123.3935	$123.39	$123.40	$123.40
Purchase #4	$152.89	8.492%	$165.8734	$165.87	$165.85	$165.90
Purchase #5	$235.92	4.775%	$247.1852	$247.19	$247.20	$247.20
Purchase #6	$95.93	7.268%	$102.9022	$102.90	$102.90	$102.90
Purchase #7	$143.50	3.350%	$148.3073	$148.31	$148.30	$148.30
7 purchase totals =	$901.67		$962.1712	$962.17	$962.20	$962.20