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	$54.83	11.756%	$61.2758	$61.28	$61.30	$61.30
Purchase #2	$116.89	4.266%	$121.8765	$121.88	$121.90	$121.90
Purchase #3	$112.48	6.160%	$119.4088	$119.41	$119.40	$119.40
Purchase #4	$133.51	9.630%	$146.367	$146.37	$146.35	$146.40
Purchase #5	$100.37	11.276%	$111.6877	$111.69	$111.70	$111.70
Purchase #6	$172.97	3.400%	$178.851	$178.85	$178.85	$178.90
Purchase #7	$77.65	3.461%	$80.3375	$80.34	$80.35	$80.30
7 purchase totals =	$768.70		$819.8043	$819.82	$819.85	$819.90