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	$114.73	5.317%	$120.8302	$120.83	$120.85	$120.80
Purchase #2	$17.94	12.452%	$20.1739	$20.17	$20.15	$20.20
Purchase #3	$188.70	11.498%	$210.3967	$210.40	$210.40	$210.40
Purchase #4	$192.50	3.608%	$199.4454	$199.45	$199.45	$199.40
Purchase #5	$129.49	12.190%	$145.2748	$145.27	$145.25	$145.30
Purchase #6	$114.30	7.715%	$123.1182	$123.12	$123.10	$123.10
Purchase #7	$77.50	7.609%	$83.397	$83.40	$83.40	$83.40
7 purchase totals =	$835.16		$902.6362	$902.64	$902.60	$902.60