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	$153.96	8.393%	$166.8819	$166.88	$166.90	$166.90
Purchase #2	$144.95	13.337%	$164.282	$164.28	$164.30	$164.30
Purchase #3	$85.63	4.620%	$89.5861	$89.59	$89.60	$89.60
Purchase #4	$54.82	12.637%	$61.7476	$61.75	$61.75	$61.70
Purchase #5	$14.77	10.852%	$16.3728	$16.37	$16.35	$16.40
Purchase #6	$235.45	3.444%	$243.5589	$243.56	$243.55	$243.60
Purchase #7	$191.80	3.439%	$198.396	$198.40	$198.40	$198.40
7 purchase totals =	$881.38		$940.8253	$940.83	$940.85	$940.90