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	$85.35	8.822%	$92.8796	$92.88	$92.90	$92.90
Purchase #2	$193.50	10.255%	$213.3434	$213.34	$213.35	$213.30
Purchase #3	$82.61	7.805%	$89.0577	$89.06	$89.05	$89.10
Purchase #4	$200.44	8.393%	$217.2629	$217.26	$217.25	$217.30
Purchase #5	$48.49	5.251%	$51.0362	$51.04	$51.05	$51.00
Purchase #6	$130.48	13.838%	$148.5358	$148.54	$148.55	$148.50
Purchase #7	$46.80	9.773%	$51.3738	$51.37	$51.35	$51.40
7 purchase totals =	$787.67		$863.4894	$863.49	$863.50	$863.50