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	$18.31	11.799%	$20.4704	$20.47	$20.45	$20.50
Purchase #2	$48.42	5.410%	$51.0395	$51.04	$51.05	$51.00
Purchase #3	$104.39	10.580%	$115.4345	$115.43	$115.45	$115.40
Purchase #4	$81.35	9.463%	$89.0482	$89.05	$89.05	$89.00
Purchase #5	$62.40	9.536%	$68.3505	$68.35	$68.35	$68.40
Purchase #6	$62.76	9.566%	$68.7636	$68.76	$68.75	$68.80
Purchase #7	$20.30	5.142%	$21.3438	$21.34	$21.35	$21.30
7 purchase totals =	$397.93		$434.4505	$434.44	$434.45	$434.40