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	$24.43	9.535%	$26.7594	$26.76	$26.75	$26.80
Purchase #2	$38.27	3.653%	$39.668	$39.67	$39.65	$39.70
Purchase #3	$97.32	6.328%	$103.4784	$103.48	$103.50	$103.50
Purchase #4	$18.89	13.806%	$21.498	$21.50	$21.50	$21.50
Purchase #5	$141.62	13.307%	$160.4654	$160.47	$160.45	$160.50
Purchase #6	$126.71	10.213%	$139.6509	$139.65	$139.65	$139.70
Purchase #7	$135.34	5.310%	$142.5266	$142.53	$142.55	$142.50
7 purchase totals =	$582.58		$634.0467	$634.06	$634.05	$634.20