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	$12.67	9.690%	$13.8977	$13.90	$13.90	$13.90
Purchase #2	$156.81	5.738%	$165.8078	$165.81	$165.80	$165.80
Purchase #3	$69.68	3.749%	$72.2923	$72.29	$72.30	$72.30
Purchase #4	$35.90	12.355%	$40.3354	$40.34	$40.35	$40.30
Purchase #5	$120.38	13.797%	$136.9888	$136.99	$137.00	$137.00
Purchase #6	$166.85	4.685%	$174.6669	$174.67	$174.65	$174.70
Purchase #7	$245.74	7.622%	$264.4703	$264.47	$264.45	$264.50
7 purchase totals =	$808.03		$868.4592	$868.47	$868.45	$868.50