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	$11.58	10.581%	$12.8053	$12.81	$12.80	$12.80
Purchase #2	$34.54	7.566%	$37.1533	$37.15	$37.15	$37.20
Purchase #3	$29.53	6.236%	$31.3715	$31.37	$31.35	$31.40
Purchase #4	$78.98	12.225%	$88.6353	$88.64	$88.65	$88.60
Purchase #5	$35.60	12.117%	$39.9137	$39.91	$39.90	$39.90
Purchase #6	$238.47	5.229%	$250.9396	$250.94	$250.95	$250.90
Purchase #7	$199.94	4.609%	$209.1552	$209.16	$209.15	$209.20
7 purchase totals =	$628.64		$669.9739	$669.98	$669.95	$670.00