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	$142.72	11.517%	$159.1571	$159.16	$159.15	$159.20
Purchase #2	$50.25	10.337%	$55.4443	$55.44	$55.45	$55.40
Purchase #3	$68.48	7.291%	$73.4729	$73.47	$73.45	$73.50
Purchase #4	$172.89	12.515%	$194.5272	$194.53	$194.55	$194.50
Purchase #5	$49.72	6.153%	$52.7793	$52.78	$52.80	$52.80
Purchase #6	$220.27	5.196%	$231.7152	$231.72	$231.70	$231.70
Purchase #7	$27.49	7.503%	$29.5526	$29.55	$29.55	$29.60
7 purchase totals =	$731.82		$796.6486	$796.65	$796.65	$796.70