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	$116.97	5.607%	$123.5285	$123.53	$123.55	$123.50
Purchase #2	$49.68	9.628%	$54.4632	$54.46	$54.45	$54.50
Purchase #3	$70.56	12.613%	$79.4597	$79.46	$79.45	$79.50
Purchase #4	$153.50	4.578%	$160.5272	$160.53	$160.55	$160.50
Purchase #5	$84.80	8.822%	$92.2811	$92.28	$92.30	$92.30
Purchase #6	$35.42	4.149%	$36.8896	$36.89	$36.90	$36.90
Purchase #7	$129.38	10.120%	$142.4733	$142.47	$142.45	$142.50
7 purchase totals =	$640.31		$689.6226	$689.62	$689.65	$689.70