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	$167.53	12.113%	$187.8229	$187.82	$187.80	$187.80
Purchase #2	$209.88	11.116%	$233.2103	$233.21	$233.20	$233.20
Purchase #3	$182.58	12.223%	$204.8968	$204.90	$204.90	$204.90
Purchase #4	$132.29	13.788%	$150.5301	$150.53	$150.55	$150.50
Purchase #5	$71.95	12.772%	$81.1395	$81.14	$81.15	$81.10
Purchase #6	$43.55	4.748%	$45.6178	$45.62	$45.60	$45.60
Purchase #7	$85.43	10.324%	$94.2498	$94.25	$94.25	$94.20
7 purchase totals =	$893.21		$997.4672	$997.47	$997.45	$997.30