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	$218.34	13.138%	$247.0255	$247.03	$247.05	$247.00
Purchase #2	$172.34	11.353%	$191.9058	$191.91	$191.90	$191.90
Purchase #3	$105.46	10.526%	$116.5607	$116.56	$116.55	$116.60
Purchase #4	$30.85	8.472%	$33.4636	$33.46	$33.45	$33.50
Purchase #5	$8.38	4.602%	$8.7656	$8.77	$8.75	$8.80
Purchase #6	$106.94	5.729%	$113.0666	$113.07	$113.05	$113.10
Purchase #7	$33.96	13.268%	$38.4658	$38.47	$38.45	$38.50
7 purchase totals =	$676.27		$749.2536	$749.27	$749.20	$749.40