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	$6.91	6.836%	$7.3824	$7.38	$7.40	$7.40
Purchase #2	$57.64	7.245%	$61.816	$61.82	$61.80	$61.80
Purchase #3	$99.43	10.567%	$109.9368	$109.94	$109.95	$109.90
Purchase #4	$213.52	5.456%	$225.1697	$225.17	$225.15	$225.20
Purchase #5	$144.30	9.195%	$157.5684	$157.57	$157.55	$157.60
Purchase #6	$97.72	7.868%	$105.4086	$105.41	$105.40	$105.40
Purchase #7	$219.28	10.293%	$241.8505	$241.85	$241.85	$241.90
7 purchase totals =	$838.80		$909.1324	$909.14	$909.10	$909.20