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	$99.79	12.563%	$112.3266	$112.33	$112.35	$112.30
Purchase #2	$80.98	5.648%	$85.5538	$85.55	$85.55	$85.60
Purchase #3	$50.95	8.378%	$55.2186	$55.22	$55.20	$55.20
Purchase #4	$66.33	4.693%	$69.4429	$69.44	$69.45	$69.40
Purchase #5	$132.89	5.667%	$140.4209	$140.42	$140.40	$140.40
Purchase #6	$121.72	10.433%	$134.419	$134.42	$134.40	$134.40
Purchase #7	$64.59	8.666%	$70.1874	$70.19	$70.20	$70.20
7 purchase totals =	$617.25		$667.5692	$667.57	$667.55	$667.50