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	$121.97	11.693%	$136.232	$136.23	$136.25	$136.20
Purchase #2	$203.69	12.310%	$228.7642	$228.76	$228.75	$228.80
Purchase #3	$99.79	11.844%	$111.6091	$111.61	$111.60	$111.60
Purchase #4	$208.96	4.562%	$218.4928	$218.49	$218.50	$218.50
Purchase #5	$72.53	4.252%	$75.614	$75.61	$75.60	$75.60
Purchase #6	$211.80	5.254%	$222.928	$222.93	$222.95	$222.90
Purchase #7	$10.34	6.330%	$10.9945	$10.99	$11.00	$11.00
7 purchase totals =	$929.08		$1,004.6346	$1,004.62	$1,004.65	$1,004.60