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	$61.36	7.863%	$66.1847	$66.18	$66.20	$66.20
Purchase #2	$47.58	3.622%	$49.3033	$49.30	$49.30	$49.30
Purchase #3	$229.85	4.824%	$240.938	$240.94	$240.95	$240.90
Purchase #4	$119.60	6.848%	$127.7902	$127.79	$127.80	$127.80
Purchase #5	$165.69	3.199%	$170.9904	$170.99	$171.00	$171.00
Purchase #6	$229.57	12.539%	$258.3558	$258.36	$258.35	$258.40
Purchase #7	$115.89	13.796%	$131.8782	$131.88	$131.90	$131.90
7 purchase totals =	$969.54		$1,045.4406	$1,045.44	$1,045.50	$1,045.50