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	$32.78	7.678%	$35.2968	$35.30	$35.30	$35.30
Purchase #2	$228.39	4.664%	$239.0421	$239.04	$239.05	$239.00
Purchase #3	$101.33	5.382%	$106.7836	$106.78	$106.80	$106.80
Purchase #4	$98.86	10.808%	$109.5448	$109.54	$109.55	$109.50
Purchase #5	$76.66	5.525%	$80.8955	$80.90	$80.90	$80.90
Purchase #6	$92.76	12.389%	$104.252	$104.25	$104.25	$104.30
Purchase #7	$132.72	9.701%	$145.5952	$145.60	$145.60	$145.60
7 purchase totals =	$763.50		$821.4100	$821.41	$821.45	$821.40