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	$131.29	5.662%	$138.7236	$138.72	$138.70	$138.70
Purchase #2	$154.59	12.774%	$174.3373	$174.34	$174.35	$174.30
Purchase #3	$138.95	11.757%	$155.2864	$155.29	$155.30	$155.30
Purchase #4	$127.26	11.205%	$141.5195	$141.52	$141.50	$141.50
Purchase #5	$74.33	12.526%	$83.6406	$83.64	$83.65	$83.60
Purchase #6	$36.70	9.113%	$40.0445	$40.04	$40.05	$40.00
Purchase #7	$172.88	3.457%	$178.8565	$178.86	$178.85	$178.90
7 purchase totals =	$836.00		$912.4084	$912.41	$912.40	$912.30