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	$38.42	3.604%	$39.8047	$39.80	$39.80	$39.80
Purchase #2	$41.67	12.822%	$47.0129	$47.01	$47.00	$47.00
Purchase #3	$104.86	4.249%	$109.3155	$109.32	$109.30	$109.30
Purchase #4	$128.55	7.463%	$138.1437	$138.14	$138.15	$138.10
Purchase #5	$209.56	11.322%	$233.2864	$233.29	$233.30	$233.30
Purchase #6	$156.81	6.816%	$167.4982	$167.50	$167.50	$167.50
Purchase #7	$13.96	3.827%	$14.4942	$14.49	$14.50	$14.50
7 purchase totals =	$693.83		$749.5556	$749.55	$749.55	$749.50