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	$162.50	12.301%	$182.4891	$182.49	$182.50	$182.50
Purchase #2	$250.77	4.191%	$261.2798	$261.28	$261.30	$261.30
Purchase #3	$170.96	12.638%	$192.5659	$192.57	$192.55	$192.60
Purchase #4	$19.58	9.261%	$21.3933	$21.39	$21.40	$21.40
Purchase #5	$81.98	12.849%	$92.5136	$92.51	$92.50	$92.50
Purchase #6	$36.82	8.744%	$40.0395	$40.04	$40.05	$40.00
Purchase #7	$162.67	10.408%	$179.6007	$179.60	$179.60	$179.60
7 purchase totals =	$885.28		$969.8819	$969.88	$969.90	$969.90