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	$158.72	9.316%	$173.5064	$173.51	$173.50	$173.50
Purchase #2	$40.38	8.739%	$43.9088	$43.91	$43.90	$43.90
Purchase #3	$199.81	11.389%	$222.5664	$222.57	$222.55	$222.60
Purchase #4	$195.39	11.810%	$218.4656	$218.47	$218.45	$218.50
Purchase #5	$113.91	8.389%	$123.4659	$123.47	$123.45	$123.50
Purchase #6	$85.35	7.297%	$91.578	$91.58	$91.60	$91.60
Purchase #7	$109.27	5.611%	$115.4011	$115.40	$115.40	$115.40
7 purchase totals =	$902.83		$988.8922	$988.91	$988.85	$989.00