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	$156.94	11.394%	$174.8217	$174.82	$174.80	$174.80
Purchase #2	$78.54	4.660%	$82.2	$82.20	$82.20	$82.20
Purchase #3	$75.29	4.375%	$78.5839	$78.58	$78.60	$78.60
Purchase #4	$143.90	6.264%	$152.9139	$152.91	$152.90	$152.90
Purchase #5	$97.61	8.145%	$105.5603	$105.56	$105.55	$105.60
Purchase #6	$71.65	10.221%	$78.9733	$78.97	$78.95	$79.00
Purchase #7	$173.86	3.778%	$180.4284	$180.43	$180.45	$180.40
7 purchase totals =	$797.79		$853.4815	$853.47	$853.45	$853.50