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	$225.69	13.397%	$255.9257	$255.93	$255.95	$255.90
Purchase #2	$40.69	13.493%	$46.1803	$46.18	$46.20	$46.20
Purchase #3	$99.90	4.761%	$104.6562	$104.66	$104.65	$104.70
Purchase #4	$202.58	9.454%	$221.7319	$221.73	$221.75	$221.70
Purchase #5	$89.60	3.568%	$92.7969	$92.80	$92.80	$92.80
Purchase #6	$55.79	12.512%	$62.7704	$62.77	$62.75	$62.80
Purchase #7	$52.97	12.663%	$59.6776	$59.68	$59.70	$59.70
7 purchase totals =	$767.22		$843.7390	$843.75	$843.80	$843.80