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	$185.73	9.795%	$203.9223	$203.92	$203.90	$203.90
Purchase #2	$120.78	9.429%	$132.1683	$132.17	$132.15	$132.20
Purchase #3	$27.82	13.685%	$31.6272	$31.63	$31.65	$31.60
Purchase #4	$42.66	5.565%	$45.034	$45.03	$45.05	$45.00
Purchase #5	$77.31	8.428%	$83.8257	$83.83	$83.85	$83.80
Purchase #6	$186.38	13.521%	$211.5804	$211.58	$211.60	$211.60
Purchase #7	$155.75	4.365%	$162.5485	$162.55	$162.55	$162.50
7 purchase totals =	$796.43		$870.7064	$870.71	$870.75	$870.60