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	$246.81	13.647%	$280.4922	$280.49	$280.50	$280.50
Purchase #2	$160.70	3.521%	$166.3582	$166.36	$166.35	$166.40
Purchase #3	$141.25	5.739%	$149.3563	$149.36	$149.35	$149.40
Purchase #4	$173.71	13.131%	$196.5199	$196.52	$196.50	$196.50
Purchase #5	$156.69	9.339%	$171.3233	$171.32	$171.30	$171.30
Purchase #6	$218.36	4.623%	$228.4548	$228.45	$228.45	$228.50
Purchase #7	$180.26	3.824%	$187.1531	$187.15	$187.15	$187.20
7 purchase totals =	$1,277.78		$1,379.6578	$1,379.65	$1,379.60	$1,379.80