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	$90.72	6.685%	$96.7846	$96.78	$96.80	$96.80
Purchase #2	$58.75	4.615%	$61.4613	$61.46	$61.45	$61.50
Purchase #3	$108.42	3.700%	$112.4315	$112.43	$112.45	$112.40
Purchase #4	$130.45	9.462%	$142.7932	$142.79	$142.80	$142.80
Purchase #5	$208.30	4.652%	$217.9901	$217.99	$218.00	$218.00
Purchase #6	$81.88	11.531%	$91.3216	$91.32	$91.30	$91.30
Purchase #7	$131.37	7.858%	$141.6931	$141.69	$141.70	$141.70
7 purchase totals =	$809.89		$864.4754	$864.46	$864.50	$864.50