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	$210.60	5.811%	$222.838	$222.84	$222.85	$222.80
Purchase #2	$129.59	10.455%	$143.1386	$143.14	$143.15	$143.10
Purchase #3	$81.77	11.687%	$91.3265	$91.33	$91.35	$91.30
Purchase #4	$11.29	10.245%	$12.4467	$12.45	$12.45	$12.40
Purchase #5	$138.71	11.506%	$154.67	$154.67	$154.65	$154.70
Purchase #6	$107.73	12.145%	$120.8138	$120.81	$120.80	$120.80
Purchase #7	$80.60	11.477%	$89.8505	$89.85	$89.85	$89.90
7 purchase totals =	$760.29		$835.0841	$835.09	$835.10	$835.00