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	$97.83	11.584%	$109.1626	$109.16	$109.15	$109.20
Purchase #2	$157.61	10.135%	$173.5838	$173.58	$173.60	$173.60
Purchase #3	$112.35	6.214%	$119.3314	$119.33	$119.35	$119.30
Purchase #4	$151.72	5.805%	$160.5273	$160.53	$160.55	$160.50
Purchase #5	$86.38	5.249%	$90.9141	$90.91	$90.90	$90.90
Purchase #6	$33.44	9.589%	$36.6466	$36.65	$36.65	$36.60
Purchase #7	$181.48	5.472%	$191.4106	$191.41	$191.40	$191.40
7 purchase totals =	$820.81		$881.5764	$881.57	$881.60	$881.50