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	$209.46	3.760%	$217.3357	$217.34	$217.35	$217.30
Purchase #2	$177.48	7.563%	$190.9028	$190.90	$190.90	$190.90
Purchase #3	$91.49	5.210%	$96.2566	$96.26	$96.25	$96.30
Purchase #4	$60.96	11.387%	$67.9015	$67.90	$67.90	$67.90
Purchase #5	$133.66	10.109%	$147.1717	$147.17	$147.15	$147.20
Purchase #6	$67.32	13.601%	$76.4762	$76.48	$76.50	$76.50
Purchase #7	$17.86	3.291%	$18.4478	$18.45	$18.45	$18.40
7 purchase totals =	$758.23		$814.4923	$814.50	$814.50	$814.50