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	$51.49	11.335%	$57.3264	$57.33	$57.35	$57.30
Purchase #2	$10.52	3.737%	$10.9131	$10.91	$10.90	$10.90
Purchase #3	$153.37	10.523%	$169.5091	$169.51	$169.50	$169.50
Purchase #4	$173.28	10.608%	$191.6615	$191.66	$191.65	$191.70
Purchase #5	$73.39	12.800%	$82.7839	$82.78	$82.80	$82.80
Purchase #6	$57.46	9.493%	$62.9147	$62.91	$62.90	$62.90
Purchase #7	$209.65	13.245%	$237.4181	$237.42	$237.40	$237.40
7 purchase totals =	$729.16		$812.5268	$812.52	$812.50	$812.50