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	$100.73	10.701%	$111.5091	$111.51	$111.50	$111.50
Purchase #2	$189.94	8.859%	$206.7668	$206.77	$206.75	$206.80
Purchase #3	$103.76	9.498%	$113.6151	$113.62	$113.60	$113.60
Purchase #4	$173.81	12.227%	$195.0617	$195.06	$195.05	$195.10
Purchase #5	$76.40	7.380%	$82.0383	$82.04	$82.05	$82.00
Purchase #6	$43.96	3.182%	$45.3588	$45.36	$45.35	$45.40
Purchase #7	$104.93	13.701%	$119.3065	$119.31	$119.30	$119.30
7 purchase totals =	$793.53		$873.6563	$873.67	$873.60	$873.70