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	$231.89	3.429%	$239.8415	$239.84	$239.85	$239.80
Purchase #2	$135.71	4.468%	$141.7735	$141.77	$141.75	$141.80
Purchase #3	$187.85	11.283%	$209.0451	$209.05	$209.05	$209.00
Purchase #4	$154.37	11.721%	$172.4637	$172.46	$172.45	$172.50
Purchase #5	$95.50	11.439%	$106.4242	$106.42	$106.40	$106.40
Purchase #6	$236.53	11.367%	$263.4164	$263.42	$263.40	$263.40
Purchase #7	$99.72	9.406%	$109.0997	$109.10	$109.10	$109.10
7 purchase totals =	$1,141.57		$1,242.0641	$1,242.06	$1,242.00	$1,242.00