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	$139.91	5.635%	$147.7939	$147.79	$147.80	$147.80
Purchase #2	$173.29	13.617%	$196.8869	$196.89	$196.90	$196.90
Purchase #3	$112.70	12.856%	$127.1887	$127.19	$127.20	$127.20
Purchase #4	$166.59	4.757%	$174.5147	$174.51	$174.50	$174.50
Purchase #5	$144.97	13.698%	$164.828	$164.83	$164.85	$164.80
Purchase #6	$194.42	10.865%	$215.5437	$215.54	$215.55	$215.50
Purchase #7	$226.28	7.578%	$243.4275	$243.43	$243.45	$243.40
7 purchase totals =	$1,158.16		$1,270.1834	$1,270.18	$1,270.25	$1,270.10