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	$9.59	4.749%	$10.0454	$10.05	$10.05	$10.00
Purchase #2	$154.66	7.853%	$166.8054	$166.81	$166.80	$166.80
Purchase #3	$101.47	8.686%	$110.2837	$110.28	$110.30	$110.30
Purchase #4	$121.46	8.387%	$131.6469	$131.65	$131.65	$131.60
Purchase #5	$29.56	9.215%	$32.284	$32.28	$32.30	$32.30
Purchase #6	$111.70	13.590%	$126.88	$126.88	$126.90	$126.90
Purchase #7	$169.71	12.824%	$191.4736	$191.47	$191.45	$191.50
7 purchase totals =	$698.15		$769.4190	$769.42	$769.45	$769.40