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	$17.71	3.421%	$18.3159	$18.32	$18.30	$18.30
Purchase #2	$86.66	11.492%	$96.619	$96.62	$96.60	$96.60
Purchase #3	$146.50	7.354%	$157.2736	$157.27	$157.25	$157.30
Purchase #4	$118.76	12.475%	$133.5753	$133.58	$133.60	$133.60
Purchase #5	$61.49	8.243%	$66.5586	$66.56	$66.55	$66.60
Purchase #6	$96.58	7.128%	$103.4642	$103.46	$103.45	$103.50
Purchase #7	$50.68	7.606%	$54.5347	$54.53	$54.55	$54.50
7 purchase totals =	$578.38		$630.3413	$630.34	$630.30	$630.40