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	$44.91	11.350%	$50.0073	$50.01	$50.00	$50.00
Purchase #2	$56.28	3.450%	$58.2217	$58.22	$58.20	$58.20
Purchase #3	$76.49	9.229%	$83.5493	$83.55	$83.55	$83.50
Purchase #4	$70.61	11.229%	$78.5388	$78.54	$78.55	$78.50
Purchase #5	$68.75	3.747%	$71.3261	$71.33	$71.35	$71.30
Purchase #6	$236.78	8.183%	$256.1557	$256.16	$256.15	$256.20
Purchase #7	$120.68	5.826%	$127.7108	$127.71	$127.70	$127.70
7 purchase totals =	$674.50		$725.5097	$725.52	$725.50	$725.40