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	$249.32	9.792%	$273.7334	$273.73	$273.75	$273.70
Purchase #2	$59.90	11.264%	$66.6471	$66.65	$66.65	$66.60
Purchase #3	$69.93	3.504%	$72.3803	$72.38	$72.40	$72.40
Purchase #4	$233.64	11.648%	$260.8544	$260.85	$260.85	$260.90
Purchase #5	$205.28	5.385%	$216.3343	$216.33	$216.35	$216.30
Purchase #6	$97.82	8.308%	$105.9469	$105.95	$105.95	$105.90
Purchase #7	$14.63	13.661%	$16.6286	$16.63	$16.65	$16.60
7 purchase totals =	$930.52		$1,012.5250	$1,012.52	$1,012.60	$1,012.40