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	$37.65	13.587%	$42.7655	$42.77	$42.75	$42.80
Purchase #2	$42.38	7.614%	$45.6068	$45.61	$45.60	$45.60
Purchase #3	$224.45	10.159%	$247.2519	$247.25	$247.25	$247.30
Purchase #4	$213.81	3.453%	$221.1929	$221.19	$221.20	$221.20
Purchase #5	$115.67	11.824%	$129.3468	$129.35	$129.35	$129.30
Purchase #6	$225.36	6.698%	$240.4546	$240.45	$240.45	$240.50
Purchase #7	$17.32	8.109%	$18.7245	$18.72	$18.70	$18.70
7 purchase totals =	$876.64		$945.3430	$945.34	$945.30	$945.40