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	$81.89	8.841%	$89.1299	$89.13	$89.15	$89.10
Purchase #2	$119.60	10.189%	$131.786	$131.79	$131.80	$131.80
Purchase #3	$5.40	7.557%	$5.8081	$5.81	$5.80	$5.80
Purchase #4	$31.52	3.208%	$32.5312	$32.53	$32.55	$32.50
Purchase #5	$24.39	6.211%	$25.9049	$25.90	$25.90	$25.90
Purchase #6	$24.38	11.298%	$27.1345	$27.13	$27.15	$27.10
Purchase #7	$46.98	3.747%	$48.7403	$48.74	$48.75	$48.70
7 purchase totals =	$334.16		$361.0349	$361.03	$361.10	$360.90