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	$136.83	7.128%	$146.5832	$146.58	$146.60	$146.60
Purchase #2	$85.97	10.293%	$94.8189	$94.82	$94.80	$94.80
Purchase #3	$145.50	8.750%	$158.2313	$158.23	$158.25	$158.20
Purchase #4	$177.39	10.558%	$196.1188	$196.12	$196.10	$196.10
Purchase #5	$85.95	5.736%	$90.8801	$90.88	$90.90	$90.90
Purchase #6	$221.68	3.375%	$229.1617	$229.16	$229.15	$229.20
Purchase #7	$173.30	13.105%	$196.011	$196.01	$196.00	$196.00
7 purchase totals =	$1,026.62		$1,111.8050	$1,111.80	$1,111.80	$1,111.80