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	$100.79	13.587%	$114.4843	$114.48	$114.50	$114.50
Purchase #2	$160.37	13.157%	$181.4699	$181.47	$181.45	$181.50
Purchase #3	$138.72	6.224%	$147.3539	$147.35	$147.35	$147.40
Purchase #4	$247.25	3.811%	$256.6727	$256.67	$256.65	$256.70
Purchase #5	$169.46	5.258%	$178.3702	$178.37	$178.35	$178.40
Purchase #6	$25.43	13.303%	$28.813	$28.81	$28.80	$28.80
Purchase #7	$118.45	11.227%	$131.7484	$131.75	$131.75	$131.70
7 purchase totals =	$960.47		$1,038.9124	$1,038.90	$1,038.85	$1,039.00