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	$79.93	6.691%	$85.2781	$85.28	$85.30	$85.30
Purchase #2	$178.33	4.128%	$185.6915	$185.69	$185.70	$185.70
Purchase #3	$187.74	12.613%	$211.4196	$211.42	$211.40	$211.40
Purchase #4	$93.87	10.156%	$103.4034	$103.40	$103.40	$103.40
Purchase #5	$171.25	4.361%	$178.7182	$178.72	$178.70	$178.70
Purchase #6	$191.83	10.695%	$212.3462	$212.35	$212.35	$212.30
Purchase #7	$147.66	11.379%	$164.4622	$164.46	$164.45	$164.50
7 purchase totals =	$1,050.61		$1,141.3192	$1,141.32	$1,141.30	$1,141.30