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	$114.42	6.258%	$121.5804	$121.58	$121.60	$121.60
Purchase #2	$46.71	12.390%	$52.4974	$52.50	$52.50	$52.50
Purchase #3	$173.41	11.109%	$192.6741	$192.67	$192.65	$192.70
Purchase #4	$31.47	10.631%	$34.8156	$34.82	$34.80	$34.80
Purchase #5	$172.86	13.526%	$196.241	$196.24	$196.25	$196.20
Purchase #6	$196.69	13.825%	$223.8824	$223.88	$223.90	$223.90
Purchase #7	$108.75	13.270%	$123.1811	$123.18	$123.20	$123.20
7 purchase totals =	$844.31		$944.8720	$944.87	$944.90	$944.90