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	$154.55	3.157%	$159.4291	$159.43	$159.45	$159.40
Purchase #2	$94.49	5.658%	$99.8362	$99.84	$99.85	$99.80
Purchase #3	$81.83	7.315%	$87.8159	$87.82	$87.80	$87.80
Purchase #4	$58.42	10.132%	$64.3391	$64.34	$64.35	$64.30
Purchase #5	$248.84	4.278%	$259.4854	$259.49	$259.50	$259.50
Purchase #6	$144.34	5.596%	$152.4173	$152.42	$152.40	$152.40
Purchase #7	$63.35	6.147%	$67.2441	$67.24	$67.25	$67.20
7 purchase totals =	$845.82		$890.5671	$890.58	$890.60	$890.40