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	$127.93	12.793%	$144.2961	$144.30	$144.30	$144.30
Purchase #2	$164.86	10.312%	$181.8604	$181.86	$181.85	$181.90
Purchase #3	$119.96	10.784%	$132.8965	$132.90	$132.90	$132.90
Purchase #4	$102.73	10.451%	$113.4663	$113.47	$113.45	$113.50
Purchase #5	$147.96	13.158%	$167.4286	$167.43	$167.45	$167.40
Purchase #6	$75.29	5.802%	$79.6583	$79.66	$79.65	$79.70
Purchase #7	$207.99	3.638%	$215.5567	$215.56	$215.55	$215.60
7 purchase totals =	$946.72		$1,035.1629	$1,035.18	$1,035.15	$1,035.30