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	$66.83	8.615%	$72.5874	$72.59	$72.60	$72.60
Purchase #2	$85.88	13.822%	$97.7503	$97.75	$97.75	$97.80
Purchase #3	$49.53	11.290%	$55.1219	$55.12	$55.10	$55.10
Purchase #4	$25.53	12.776%	$28.7917	$28.79	$28.80	$28.80
Purchase #5	$63.79	4.107%	$66.4099	$66.41	$66.40	$66.40
Purchase #6	$181.43	11.795%	$202.8297	$202.83	$202.85	$202.80
Purchase #7	$102.80	13.127%	$116.2946	$116.29	$116.30	$116.30
7 purchase totals =	$575.79		$639.7855	$639.78	$639.80	$639.80