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	$141.54	6.469%	$150.6962	$150.70	$150.70	$150.70
Purchase #2	$205.60	12.503%	$231.3062	$231.31	$231.30	$231.30
Purchase #3	$34.36	9.447%	$37.606	$37.61	$37.60	$37.60
Purchase #4	$97.83	11.209%	$108.7958	$108.80	$108.80	$108.80
Purchase #5	$128.33	4.340%	$133.8995	$133.90	$133.90	$133.90
Purchase #6	$225.95	13.538%	$256.5391	$256.54	$256.55	$256.50
Purchase #7	$9.76	3.774%	$10.1283	$10.13	$10.15	$10.10
7 purchase totals =	$843.37		$928.9711	$928.99	$929.00	$928.90