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	$248.47	6.304%	$264.1335	$264.13	$264.15	$264.10
Purchase #2	$139.51	4.664%	$146.0167	$146.02	$146.00	$146.00
Purchase #3	$172.25	7.319%	$184.857	$184.86	$184.85	$184.90
Purchase #4	$78.34	10.619%	$86.6589	$86.66	$86.65	$86.70
Purchase #5	$223.54	7.737%	$240.8353	$240.84	$240.85	$240.80
Purchase #6	$23.44	10.653%	$25.9371	$25.94	$25.95	$25.90
Purchase #7	$151.54	6.298%	$161.084	$161.08	$161.10	$161.10
7 purchase totals =	$1,037.09		$1,109.5225	$1,109.53	$1,109.55	$1,109.50