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	$54.48	8.330%	$59.0182	$59.02	$59.00	$59.00
Purchase #2	$233.75	5.289%	$246.113	$246.11	$246.10	$246.10
Purchase #3	$232.68	8.478%	$252.4066	$252.41	$252.40	$252.40
Purchase #4	$192.69	4.193%	$200.7695	$200.77	$200.75	$200.80
Purchase #5	$59.63	9.678%	$65.401	$65.40	$65.40	$65.40
Purchase #6	$123.96	12.635%	$139.6223	$139.62	$139.60	$139.60
Purchase #7	$103.72	12.159%	$116.3313	$116.33	$116.35	$116.30
7 purchase totals =	$1,000.91		$1,079.6619	$1,079.66	$1,079.60	$1,079.60