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	$58.46	13.666%	$66.4491	$66.45	$66.45	$66.40
Purchase #2	$246.97	12.778%	$278.5278	$278.53	$278.55	$278.50
Purchase #3	$222.46	6.728%	$237.4271	$237.43	$237.45	$237.40
Purchase #4	$245.50	8.401%	$266.1245	$266.12	$266.10	$266.10
Purchase #5	$52.61	13.842%	$59.8923	$59.89	$59.90	$59.90
Purchase #6	$76.39	6.495%	$81.3515	$81.35	$81.35	$81.40
Purchase #7	$136.67	13.246%	$154.7733	$154.77	$154.75	$154.80
7 purchase totals =	$1,039.06		$1,144.5456	$1,144.54	$1,144.55	$1,144.50