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	$7.58	4.451%	$7.9174	$7.92	$7.90	$7.90
Purchase #2	$97.34	12.504%	$109.5114	$109.51	$109.50	$109.50
Purchase #3	$180.34	5.621%	$190.4769	$190.48	$190.50	$190.50
Purchase #4	$96.99	3.682%	$100.5612	$100.56	$100.55	$100.60
Purchase #5	$96.31	5.776%	$101.8729	$101.87	$101.85	$101.90
Purchase #6	$19.77	7.328%	$21.2187	$21.22	$21.20	$21.20
Purchase #7	$119.90	3.517%	$124.1169	$124.12	$124.10	$124.10
7 purchase totals =	$618.23		$655.6754	$655.68	$655.60	$655.70