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	$36.28	8.127%	$39.2285	$39.23	$39.25	$39.20
Purchase #2	$156.72	10.120%	$172.5801	$172.58	$172.60	$172.60
Purchase #3	$205.29	10.438%	$226.7182	$226.72	$226.70	$226.70
Purchase #4	$89.43	12.419%	$100.5363	$100.54	$100.55	$100.50
Purchase #5	$80.46	6.863%	$85.982	$85.98	$86.00	$86.00
Purchase #6	$96.71	8.191%	$104.6315	$104.63	$104.65	$104.60
Purchase #7	$82.97	12.240%	$93.1255	$93.13	$93.15	$93.10
7 purchase totals =	$747.86		$822.8021	$822.81	$822.90	$822.70