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	$233.28	11.277%	$259.587	$259.59	$259.60	$259.60
Purchase #2	$28.90	10.610%	$31.9663	$31.97	$31.95	$32.00
Purchase #3	$63.95	13.179%	$72.378	$72.38	$72.40	$72.40
Purchase #4	$235.41	10.685%	$260.5636	$260.56	$260.55	$260.60
Purchase #5	$166.82	3.614%	$172.8489	$172.85	$172.85	$172.80
Purchase #6	$55.57	5.326%	$58.5297	$58.53	$58.55	$58.50
Purchase #7	$39.72	10.444%	$43.8684	$43.87	$43.85	$43.90
7 purchase totals =	$823.65		$899.7419	$899.75	$899.75	$899.80