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	$35.36	8.830%	$38.4823	$38.48	$38.50	$38.50
Purchase #2	$72.81	10.213%	$80.2461	$80.25	$80.25	$80.20
Purchase #3	$103.43	8.182%	$111.8926	$111.89	$111.90	$111.90
Purchase #4	$42.54	4.308%	$44.3726	$44.37	$44.35	$44.40
Purchase #5	$241.97	6.340%	$257.3109	$257.31	$257.30	$257.30
Purchase #6	$143.50	7.249%	$153.9023	$153.90	$153.90	$153.90
Purchase #7	$133.72	12.105%	$149.9068	$149.91	$149.90	$149.90
7 purchase totals =	$773.33		$836.1136	$836.11	$836.10	$836.10