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	$209.69	9.408%	$229.4176	$229.42	$229.40	$229.40
Purchase #2	$79.29	4.469%	$82.8335	$82.83	$82.85	$82.80
Purchase #3	$225.68	6.798%	$241.0217	$241.02	$241.00	$241.00
Purchase #4	$196.85	13.258%	$222.9484	$222.95	$222.95	$222.90
Purchase #5	$100.25	11.508%	$111.7868	$111.79	$111.80	$111.80
Purchase #6	$217.81	4.177%	$226.9079	$226.91	$226.90	$226.90
Purchase #7	$154.57	7.159%	$165.6357	$165.64	$165.65	$165.60
7 purchase totals =	$1,184.14		$1,280.5516	$1,280.56	$1,280.55	$1,280.40