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	$81.36	9.506%	$89.0941	$89.09	$89.10	$89.10
Purchase #2	$125.33	9.194%	$136.8528	$136.85	$136.85	$136.90
Purchase #3	$206.59	5.162%	$217.2542	$217.25	$217.25	$217.30
Purchase #4	$88.64	12.536%	$99.7519	$99.75	$99.75	$99.80
Purchase #5	$203.40	13.612%	$231.0868	$231.09	$231.10	$231.10
Purchase #6	$141.90	10.153%	$156.3071	$156.31	$156.30	$156.30
Purchase #7	$62.95	11.740%	$70.3403	$70.34	$70.35	$70.30
7 purchase totals =	$910.17		$1,000.6872	$1,000.68	$1,000.70	$1,000.80