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	$19.31	7.491%	$20.7565	$20.76	$20.75	$20.80
Purchase #2	$81.86	12.498%	$92.0909	$92.09	$92.10	$92.10
Purchase #3	$42.42	10.824%	$47.0115	$47.01	$47.00	$47.00
Purchase #4	$169.94	10.404%	$187.6206	$187.62	$187.60	$187.60
Purchase #5	$30.43	6.374%	$32.3696	$32.37	$32.35	$32.40
Purchase #6	$49.53	9.519%	$54.2448	$54.24	$54.25	$54.20
Purchase #7	$123.25	6.673%	$131.4745	$131.47	$131.45	$131.50
7 purchase totals =	$516.74		$565.5684	$565.56	$565.50	$565.60