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	$125.65	9.685%	$137.8192	$137.82	$137.80	$137.80
Purchase #2	$80.68	5.492%	$85.1109	$85.11	$85.10	$85.10
Purchase #3	$19.90	5.798%	$21.0538	$21.05	$21.05	$21.10
Purchase #4	$182.85	4.160%	$190.4566	$190.46	$190.45	$190.50
Purchase #5	$148.71	5.591%	$157.0244	$157.02	$157.00	$157.00
Purchase #6	$91.51	8.523%	$99.3094	$99.31	$99.30	$99.30
Purchase #7	$203.55	6.621%	$217.027	$217.03	$217.05	$217.00
7 purchase totals =	$852.85		$907.8013	$907.80	$907.75	$907.80