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	$14.56	6.771%	$15.5459	$15.55	$15.55	$15.50
Purchase #2	$111.91	10.254%	$123.3853	$123.39	$123.40	$123.40
Purchase #3	$107.48	11.786%	$120.1476	$120.15	$120.15	$120.10
Purchase #4	$97.75	11.761%	$109.2464	$109.25	$109.25	$109.20
Purchase #5	$70.33	7.399%	$75.5337	$75.53	$75.55	$75.50
Purchase #6	$60.34	5.382%	$63.5875	$63.59	$63.60	$63.60
Purchase #7	$17.61	11.275%	$19.5955	$19.60	$19.60	$19.60
7 purchase totals =	$479.98		$527.0419	$527.06	$527.10	$526.90