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	$82.64	12.408%	$92.894	$92.89	$92.90	$92.90
Purchase #2	$203.59	12.520%	$229.0795	$229.08	$229.10	$229.10
Purchase #3	$130.57	11.651%	$145.7827	$145.78	$145.80	$145.80
Purchase #4	$41.34	6.849%	$44.1714	$44.17	$44.15	$44.20
Purchase #5	$136.40	5.311%	$143.6442	$143.64	$143.65	$143.60
Purchase #6	$241.98	6.156%	$256.8763	$256.88	$256.90	$256.90
Purchase #7	$99.51	7.369%	$106.8429	$106.84	$106.85	$106.80
7 purchase totals =	$936.03		$1,019.2910	$1,019.28	$1,019.35	$1,019.30