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	$28.32	13.771%	$32.2199	$32.22	$32.20	$32.20
Purchase #2	$82.84	10.763%	$91.7561	$91.76	$91.75	$91.80
Purchase #3	$223.26	7.556%	$240.1295	$240.13	$240.15	$240.10
Purchase #4	$194.32	12.156%	$217.9415	$217.94	$217.95	$217.90
Purchase #5	$25.68	12.592%	$28.9136	$28.91	$28.90	$28.90
Purchase #6	$96.83	9.211%	$105.749	$105.75	$105.75	$105.70
Purchase #7	$186.32	4.602%	$194.8944	$194.89	$194.90	$194.90
7 purchase totals =	$837.57		$911.6040	$911.60	$911.60	$911.50