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	$126.38	4.781%	$132.4222	$132.42	$132.40	$132.40
Purchase #2	$109.70	10.235%	$120.9278	$120.93	$120.95	$120.90
Purchase #3	$11.79	13.447%	$13.3754	$13.38	$13.40	$13.40
Purchase #4	$38.81	4.205%	$40.442	$40.44	$40.45	$40.40
Purchase #5	$75.33	10.622%	$83.3316	$83.33	$83.35	$83.30
Purchase #6	$27.46	4.162%	$28.6029	$28.60	$28.60	$28.60
Purchase #7	$134.88	11.751%	$150.7297	$150.73	$150.75	$150.70
7 purchase totals =	$524.35		$569.8316	$569.83	$569.90	$569.70