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	$170.60	12.759%	$192.3669	$192.37	$192.35	$192.40
Purchase #2	$128.78	11.574%	$143.685	$143.69	$143.70	$143.70
Purchase #3	$136.74	3.567%	$141.6175	$141.62	$141.60	$141.60
Purchase #4	$60.73	10.583%	$67.1571	$67.16	$67.15	$67.20
Purchase #5	$158.38	6.622%	$168.8679	$168.87	$168.85	$168.90
Purchase #6	$96.92	8.819%	$105.4674	$105.47	$105.45	$105.50
Purchase #7	$39.71	5.489%	$41.8897	$41.89	$41.90	$41.90
7 purchase totals =	$791.86		$861.0515	$861.07	$861.00	$861.20