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	$177.33	6.852%	$189.4807	$189.48	$189.50	$189.50
Purchase #2	$13.99	10.157%	$15.411	$15.41	$15.40	$15.40
Purchase #3	$219.37	4.806%	$229.9129	$229.91	$229.90	$229.90
Purchase #4	$119.29	5.456%	$125.7985	$125.80	$125.80	$125.80
Purchase #5	$144.82	5.588%	$152.9125	$152.91	$152.90	$152.90
Purchase #6	$91.84	9.544%	$100.6052	$100.61	$100.60	$100.60
Purchase #7	$249.47	12.804%	$281.4121	$281.41	$281.40	$281.40
7 purchase totals =	$1,016.11		$1,095.5329	$1,095.53	$1,095.50	$1,095.50