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	$232.34	9.821%	$255.1581	$255.16	$255.15	$255.20
Purchase #2	$185.31	3.472%	$191.744	$191.74	$191.75	$191.70
Purchase #3	$237.45	11.607%	$265.0108	$265.01	$265.00	$265.00
Purchase #4	$222.73	4.764%	$233.3409	$233.34	$233.35	$233.30
Purchase #5	$154.81	10.691%	$171.3607	$171.36	$171.35	$171.40
Purchase #6	$113.98	5.135%	$119.8329	$119.83	$119.85	$119.80
Purchase #7	$153.52	3.168%	$158.3835	$158.38	$158.40	$158.40
7 purchase totals =	$1,300.14		$1,394.8309	$1,394.82	$1,394.85	$1,394.80