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	$109.77	13.294%	$124.3628	$124.36	$124.35	$124.40
Purchase #2	$164.48	5.450%	$173.4442	$173.44	$173.45	$173.40
Purchase #3	$119.56	12.520%	$134.5289	$134.53	$134.55	$134.50
Purchase #4	$145.32	7.746%	$156.5765	$156.58	$156.60	$156.60
Purchase #5	$166.95	3.475%	$172.7515	$172.75	$172.75	$172.80
Purchase #6	$123.60	13.453%	$140.2279	$140.23	$140.25	$140.20
Purchase #7	$82.92	10.745%	$91.8298	$91.83	$91.85	$91.80
7 purchase totals =	$912.60		$993.7216	$993.72	$993.80	$993.70