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	$123.46	12.134%	$138.4406	$138.44	$138.45	$138.40
Purchase #2	$119.52	6.678%	$127.5015	$127.50	$127.50	$127.50
Purchase #3	$14.52	5.846%	$15.3688	$15.37	$15.35	$15.40
Purchase #4	$134.73	7.866%	$145.3279	$145.33	$145.35	$145.30
Purchase #5	$200.77	9.234%	$219.3091	$219.31	$219.30	$219.30
Purchase #6	$79.60	13.126%	$90.0483	$90.05	$90.05	$90.00
Purchase #7	$245.32	10.837%	$271.9053	$271.91	$271.90	$271.90
7 purchase totals =	$917.92		$1,007.9015	$1,007.91	$1,007.90	$1,007.80