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	$49.91	11.768%	$55.7834	$55.78	$55.80	$55.80
Purchase #2	$243.39	13.238%	$275.61	$275.61	$275.60	$275.60
Purchase #3	$112.99	3.133%	$116.53	$116.53	$116.55	$116.50
Purchase #4	$198.93	3.826%	$206.5411	$206.54	$206.55	$206.50
Purchase #5	$134.70	4.502%	$140.7642	$140.76	$140.75	$140.80
Purchase #6	$177.81	7.393%	$190.9555	$190.96	$190.95	$191.00
Purchase #7	$93.49	6.723%	$99.7753	$99.78	$99.80	$99.80
7 purchase totals =	$1,011.22		$1,085.9595	$1,085.96	$1,086.00	$1,086.00