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	$58.54	13.386%	$66.3762	$66.38	$66.40	$66.40
Purchase #2	$142.40	13.690%	$161.8946	$161.89	$161.90	$161.90
Purchase #3	$170.88	10.868%	$189.4512	$189.45	$189.45	$189.50
Purchase #4	$230.30	6.194%	$244.5648	$244.56	$244.55	$244.60
Purchase #5	$86.61	6.732%	$92.4406	$92.44	$92.45	$92.40
Purchase #6	$139.81	6.451%	$148.8291	$148.83	$148.85	$148.80
Purchase #7	$209.36	9.778%	$229.8312	$229.83	$229.85	$229.80
7 purchase totals =	$1,037.90		$1,133.3877	$1,133.38	$1,133.45	$1,133.40