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	$15.50	5.198%	$16.3057	$16.31	$16.30	$16.30
Purchase #2	$86.55	4.543%	$90.482	$90.48	$90.50	$90.50
Purchase #3	$108.56	8.705%	$118.0101	$118.01	$118.00	$118.00
Purchase #4	$35.87	11.174%	$39.8781	$39.88	$39.90	$39.90
Purchase #5	$46.57	9.118%	$50.8163	$50.82	$50.80	$50.80
Purchase #6	$151.65	8.487%	$164.5205	$164.52	$164.50	$164.50
Purchase #7	$163.79	13.718%	$186.2587	$186.26	$186.25	$186.30
7 purchase totals =	$608.49		$666.2714	$666.28	$666.25	$666.30