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	$58.68	12.745%	$66.1588	$66.16	$66.15	$66.20
Purchase #2	$32.58	13.397%	$36.9447	$36.94	$36.95	$36.90
Purchase #3	$186.74	5.156%	$196.3683	$196.37	$196.35	$196.40
Purchase #4	$238.95	12.503%	$268.8259	$268.83	$268.85	$268.80
Purchase #5	$189.50	13.525%	$215.1299	$215.13	$215.15	$215.10
Purchase #6	$95.60	4.211%	$99.6257	$99.63	$99.65	$99.60
Purchase #7	$207.72	6.293%	$220.7918	$220.79	$220.80	$220.80
7 purchase totals =	$1,009.77		$1,103.8451	$1,103.85	$1,103.90	$1,103.80