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	$152.50	13.170%	$172.5843	$172.58	$172.60	$172.60
Purchase #2	$208.61	12.599%	$234.8928	$234.89	$234.90	$234.90
Purchase #3	$63.55	5.374%	$66.9652	$66.97	$66.95	$67.00
Purchase #4	$7.29	7.580%	$7.8426	$7.84	$7.85	$7.80
Purchase #5	$75.44	10.214%	$83.1454	$83.15	$83.15	$83.10
Purchase #6	$24.40	13.278%	$27.6398	$27.64	$27.65	$27.60
Purchase #7	$96.80	8.256%	$104.7918	$104.79	$104.80	$104.80
7 purchase totals =	$628.59		$697.8619	$697.86	$697.90	$697.80