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	$35.76	11.183%	$39.759	$39.76	$39.75	$39.80
Purchase #2	$246.87	11.563%	$275.4156	$275.42	$275.40	$275.40
Purchase #3	$38.70	10.679%	$42.8328	$42.83	$42.85	$42.80
Purchase #4	$215.81	13.805%	$245.6026	$245.60	$245.60	$245.60
Purchase #5	$236.42	10.494%	$261.2299	$261.23	$261.25	$261.20
Purchase #6	$11.78	6.272%	$12.5188	$12.52	$12.50	$12.50
Purchase #7	$227.41	6.545%	$242.294	$242.29	$242.30	$242.30
7 purchase totals =	$1,012.75		$1,119.6527	$1,119.65	$1,119.65	$1,119.60