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	$135.25	8.147%	$146.2688	$146.27	$146.25	$146.30
Purchase #2	$113.58	12.608%	$127.9002	$127.90	$127.90	$127.90
Purchase #3	$94.41	10.190%	$104.0304	$104.03	$104.05	$104.00
Purchase #4	$187.52	13.224%	$212.3176	$212.32	$212.30	$212.30
Purchase #5	$97.33	12.438%	$109.4359	$109.44	$109.45	$109.40
Purchase #6	$101.28	11.719%	$113.149	$113.15	$113.15	$113.10
Purchase #7	$85.87	11.273%	$95.5501	$95.55	$95.55	$95.60
7 purchase totals =	$815.24		$908.6520	$908.66	$908.65	$908.60