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	$23.47	8.594%	$25.487	$25.49	$25.50	$25.50
Purchase #2	$131.34	11.112%	$145.9345	$145.93	$145.95	$145.90
Purchase #3	$211.36	10.279%	$233.0857	$233.09	$233.10	$233.10
Purchase #4	$238.42	4.159%	$248.3359	$248.34	$248.35	$248.30
Purchase #5	$193.48	12.626%	$217.9088	$217.91	$217.90	$217.90
Purchase #6	$100.89	10.631%	$111.6156	$111.62	$111.60	$111.60
Purchase #7	$193.33	3.408%	$199.9187	$199.92	$199.90	$199.90
7 purchase totals =	$1,092.29		$1,182.2862	$1,182.30	$1,182.30	$1,182.20