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	$81.33	11.422%	$90.6195	$90.62	$90.60	$90.60
Purchase #2	$52.34	3.245%	$54.0384	$54.04	$54.05	$54.00
Purchase #3	$44.60	11.267%	$49.6251	$49.63	$49.65	$49.60
Purchase #4	$34.66	12.274%	$38.9142	$38.91	$38.90	$38.90
Purchase #5	$76.46	11.628%	$85.3508	$85.35	$85.35	$85.40
Purchase #6	$28.65	5.207%	$30.1418	$30.14	$30.15	$30.10
Purchase #7	$81.45	12.483%	$91.6174	$91.62	$91.60	$91.60
7 purchase totals =	$399.49		$440.3072	$440.31	$440.30	$440.20