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	$51.69	12.383%	$58.0908	$58.09	$58.10	$58.10
Purchase #2	$239.79	9.443%	$262.4334	$262.43	$262.45	$262.40
Purchase #3	$158.70	13.328%	$179.8515	$179.85	$179.85	$179.90
Purchase #4	$250.67	12.386%	$281.718	$281.72	$281.70	$281.70
Purchase #5	$225.30	5.867%	$238.5184	$238.52	$238.50	$238.50
Purchase #6	$188.47	6.295%	$200.3342	$200.33	$200.35	$200.30
Purchase #7	$28.75	11.626%	$32.0925	$32.09	$32.10	$32.10
7 purchase totals =	$1,143.37		$1,253.0388	$1,253.03	$1,253.05	$1,253.00