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	$123.34	10.572%	$136.3795	$136.38	$136.40	$136.40
Purchase #2	$91.30	7.830%	$98.4488	$98.45	$98.45	$98.40
Purchase #3	$68.28	12.659%	$76.9236	$76.92	$76.90	$76.90
Purchase #4	$234.87	10.415%	$259.3317	$259.33	$259.35	$259.30
Purchase #5	$166.78	3.307%	$172.2954	$172.30	$172.30	$172.30
Purchase #6	$214.55	3.490%	$222.0378	$222.04	$222.05	$222.00
Purchase #7	$163.68	5.422%	$172.5547	$172.55	$172.55	$172.60
7 purchase totals =	$1,062.80		$1,137.9715	$1,137.97	$1,138.00	$1,137.90