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	$122.57	12.854%	$138.3251	$138.33	$138.35	$138.30
Purchase #2	$170.91	10.633%	$189.0829	$189.08	$189.10	$189.10
Purchase #3	$58.40	5.565%	$61.65	$61.65	$61.65	$61.70
Purchase #4	$80.83	10.769%	$89.5346	$89.53	$89.55	$89.50
Purchase #5	$169.45	13.213%	$191.8394	$191.84	$191.85	$191.80
Purchase #6	$111.37	10.487%	$123.0494	$123.05	$123.05	$123.00
Purchase #7	$176.89	9.140%	$193.0577	$193.06	$193.05	$193.10
7 purchase totals =	$890.42		$986.5391	$986.54	$986.60	$986.50