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	$52.35	5.805%	$55.3889	$55.39	$55.40	$55.40
Purchase #2	$132.52	4.793%	$138.8717	$138.87	$138.85	$138.90
Purchase #3	$145.49	10.289%	$160.4595	$160.46	$160.45	$160.50
Purchase #4	$133.67	6.473%	$142.3225	$142.32	$142.30	$142.30
Purchase #5	$111.55	4.408%	$116.4671	$116.47	$116.45	$116.50
Purchase #6	$34.45	3.116%	$35.5235	$35.52	$35.50	$35.50
Purchase #7	$130.55	9.419%	$142.8465	$142.85	$142.85	$142.80
7 purchase totals =	$740.58		$791.8797	$791.88	$791.80	$791.90