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	$250.52	11.693%	$279.8133	$279.81	$279.80	$279.80
Purchase #2	$250.63	12.374%	$281.643	$281.64	$281.65	$281.60
Purchase #3	$189.33	13.574%	$215.0297	$215.03	$215.05	$215.00
Purchase #4	$221.87	13.402%	$251.605	$251.61	$251.60	$251.60
Purchase #5	$35.73	7.414%	$38.379	$38.38	$38.40	$38.40
Purchase #6	$40.72	4.107%	$42.3924	$42.39	$42.40	$42.40
Purchase #7	$200.76	13.805%	$228.4749	$228.47	$228.45	$228.50
7 purchase totals =	$1,189.56		$1,337.3373	$1,337.33	$1,337.35	$1,337.30