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	$227.94	12.710%	$256.9112	$256.91	$256.90	$256.90
Purchase #2	$165.46	3.826%	$171.7905	$171.79	$171.80	$171.80
Purchase #3	$43.43	12.488%	$48.8535	$48.85	$48.85	$48.90
Purchase #4	$20.49	6.313%	$21.7835	$21.78	$21.80	$21.80
Purchase #5	$197.53	4.486%	$206.3912	$206.39	$206.40	$206.40
Purchase #6	$61.42	6.511%	$65.4191	$65.42	$65.40	$65.40
Purchase #7	$249.48	12.543%	$280.7723	$280.77	$280.75	$280.80
7 purchase totals =	$965.75		$1,051.9213	$1,051.91	$1,051.90	$1,052.00