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	$103.46	12.233%	$116.1163	$116.12	$116.10	$116.10
Purchase #2	$148.67	7.201%	$159.3757	$159.38	$159.40	$159.40
Purchase #3	$55.87	11.542%	$62.3185	$62.32	$62.30	$62.30
Purchase #4	$78.85	8.597%	$85.6287	$85.63	$85.65	$85.60
Purchase #5	$153.89	8.610%	$167.1399	$167.14	$167.15	$167.10
Purchase #6	$232.45	11.603%	$259.4212	$259.42	$259.40	$259.40
Purchase #7	$217.96	12.359%	$244.8977	$244.90	$244.90	$244.90
7 purchase totals =	$991.15		$1,094.8980	$1,094.91	$1,094.90	$1,094.80