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	$242.45	12.498%	$272.7514	$272.75	$272.75	$272.80
Purchase #2	$186.76	5.433%	$196.9067	$196.91	$196.90	$196.90
Purchase #3	$136.42	13.276%	$154.5311	$154.53	$154.55	$154.50
Purchase #4	$30.25	8.777%	$32.905	$32.91	$32.90	$32.90
Purchase #5	$198.52	4.389%	$207.233	$207.23	$207.25	$207.20
Purchase #6	$143.98	10.395%	$158.9467	$158.95	$158.95	$158.90
Purchase #7	$159.32	5.855%	$168.6482	$168.65	$168.65	$168.60
7 purchase totals =	$1,097.70		$1,191.9221	$1,191.93	$1,191.95	$1,191.80