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	$227.57	12.601%	$256.2461	$256.25	$256.25	$256.20
Purchase #2	$142.67	10.424%	$157.5419	$157.54	$157.55	$157.50
Purchase #3	$85.74	5.128%	$90.1367	$90.14	$90.15	$90.10
Purchase #4	$87.63	12.187%	$98.3095	$98.31	$98.30	$98.30
Purchase #5	$215.57	12.123%	$241.7036	$241.70	$241.70	$241.70
Purchase #6	$125.31	11.432%	$139.6354	$139.64	$139.65	$139.60
Purchase #7	$153.68	13.523%	$174.4621	$174.46	$174.45	$174.50
7 purchase totals =	$1,038.17		$1,158.0353	$1,158.04	$1,158.05	$1,157.90