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	$37.34	3.857%	$38.7802	$38.78	$38.80	$38.80
Purchase #2	$112.53	7.207%	$120.64	$120.64	$120.65	$120.60
Purchase #3	$139.86	7.251%	$150.0012	$150.00	$150.00	$150.00
Purchase #4	$81.51	11.605%	$90.9692	$90.97	$90.95	$91.00
Purchase #5	$237.49	11.819%	$265.5589	$265.56	$265.55	$265.60
Purchase #6	$183.37	10.605%	$202.8164	$202.82	$202.80	$202.80
Purchase #7	$173.52	11.146%	$192.8605	$192.86	$192.85	$192.90
7 purchase totals =	$965.62		$1,061.6264	$1,061.63	$1,061.60	$1,061.70