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	$34.94	12.497%	$39.3065	$39.31	$39.30	$39.30
Purchase #2	$38.90	3.621%	$40.3086	$40.31	$40.30	$40.30
Purchase #3	$56.33	8.780%	$61.2758	$61.28	$61.30	$61.30
Purchase #4	$99.68	11.469%	$111.1123	$111.11	$111.10	$111.10
Purchase #5	$100.86	13.676%	$114.6536	$114.65	$114.65	$114.70
Purchase #6	$44.30	11.848%	$49.5487	$49.55	$49.55	$49.50
Purchase #7	$183.25	9.569%	$200.7852	$200.79	$200.80	$200.80
7 purchase totals =	$558.26		$616.9907	$617.00	$617.00	$617.00