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	$128.69	10.644%	$142.3878	$142.39	$142.40	$142.40
Purchase #2	$108.40	4.360%	$113.1262	$113.13	$113.15	$113.10
Purchase #3	$141.60	10.394%	$156.3179	$156.32	$156.30	$156.30
Purchase #4	$185.62	10.240%	$204.6275	$204.63	$204.65	$204.60
Purchase #5	$53.28	11.281%	$59.2905	$59.29	$59.30	$59.30
Purchase #6	$173.87	13.169%	$196.7669	$196.77	$196.75	$196.80
Purchase #7	$98.69	13.127%	$111.645	$111.65	$111.65	$111.60
7 purchase totals =	$890.15		$984.1618	$984.18	$984.20	$984.10