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	$215.32	3.450%	$222.7485	$222.75	$222.75	$222.70
Purchase #2	$45.82	7.342%	$49.1841	$49.18	$49.20	$49.20
Purchase #3	$80.44	11.387%	$89.5997	$89.60	$89.60	$89.60
Purchase #4	$218.28	4.669%	$228.4715	$228.47	$228.45	$228.50
Purchase #5	$111.69	3.723%	$115.8482	$115.85	$115.85	$115.80
Purchase #6	$6.64	12.519%	$7.4713	$7.47	$7.45	$7.50
Purchase #7	$191.70	4.228%	$199.8051	$199.81	$199.80	$199.80
7 purchase totals =	$869.89		$913.1284	$913.13	$913.10	$913.10