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	$10.51	10.321%	$11.5947	$11.59	$11.60	$11.60
Purchase #2	$11.56	12.111%	$12.96	$12.96	$12.95	$13.00
Purchase #3	$109.88	7.831%	$118.4847	$118.48	$118.50	$118.50
Purchase #4	$199.75	11.459%	$222.6394	$222.64	$222.65	$222.60
Purchase #5	$128.32	8.853%	$139.6802	$139.68	$139.70	$139.70
Purchase #6	$133.68	13.352%	$151.529	$151.53	$151.55	$151.50
Purchase #7	$171.40	8.243%	$185.5285	$185.53	$185.55	$185.50
7 purchase totals =	$765.10		$842.4165	$842.41	$842.50	$842.40