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	$245.46	9.636%	$269.1125	$269.11	$269.10	$269.10
Purchase #2	$73.57	7.250%	$78.9038	$78.90	$78.90	$78.90
Purchase #3	$37.87	7.229%	$40.6076	$40.61	$40.60	$40.60
Purchase #4	$35.72	8.498%	$38.7555	$38.76	$38.75	$38.80
Purchase #5	$221.29	6.868%	$236.4882	$236.49	$236.50	$236.50
Purchase #6	$13.97	3.198%	$14.4168	$14.42	$14.40	$14.40
Purchase #7	$134.95	4.487%	$141.0052	$141.01	$141.00	$141.00
7 purchase totals =	$762.83		$819.2896	$819.30	$819.25	$819.30