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	$54.46	5.746%	$57.5893	$57.59	$57.60	$57.60
Purchase #2	$140.26	13.810%	$159.6299	$159.63	$159.65	$159.60
Purchase #3	$119.56	13.779%	$136.0342	$136.03	$136.05	$136.00
Purchase #4	$188.70	9.634%	$206.8794	$206.88	$206.90	$206.90
Purchase #5	$103.32	5.616%	$109.1225	$109.12	$109.10	$109.10
Purchase #6	$25.30	7.659%	$27.2377	$27.24	$27.25	$27.20
Purchase #7	$134.72	11.472%	$150.1751	$150.18	$150.20	$150.20
7 purchase totals =	$766.32		$846.6681	$846.67	$846.75	$846.60