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	$249.71	3.120%	$257.501	$257.50	$257.50	$257.50
Purchase #2	$107.65	10.636%	$119.0997	$119.10	$119.10	$119.10
Purchase #3	$187.92	4.771%	$196.8857	$196.89	$196.90	$196.90
Purchase #4	$156.41	10.559%	$172.9253	$172.93	$172.95	$172.90
Purchase #5	$50.95	6.736%	$54.382	$54.38	$54.40	$54.40
Purchase #6	$211.93	12.649%	$238.737	$238.74	$238.75	$238.70
Purchase #7	$204.48	13.432%	$231.9458	$231.95	$231.95	$231.90
7 purchase totals =	$1,169.05		$1,271.4765	$1,271.49	$1,271.55	$1,271.40