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	$102.84	4.490%	$107.4575	$107.46	$107.45	$107.50
Purchase #2	$34.64	10.757%	$38.3662	$38.37	$38.35	$38.40
Purchase #3	$168.70	13.444%	$191.38	$191.38	$191.40	$191.40
Purchase #4	$82.34	8.228%	$89.1149	$89.11	$89.10	$89.10
Purchase #5	$13.45	12.112%	$15.0791	$15.08	$15.10	$15.10
Purchase #6	$72.30	12.469%	$81.3151	$81.32	$81.30	$81.30
Purchase #7	$50.79	13.691%	$57.7437	$57.74	$57.75	$57.70
7 purchase totals =	$525.06		$580.4565	$580.46	$580.45	$580.50