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	$186.76	10.506%	$206.381	$206.38	$206.40	$206.40
Purchase #2	$95.72	12.161%	$107.3605	$107.36	$107.35	$107.40
Purchase #3	$163.94	5.210%	$172.4813	$172.48	$172.50	$172.50
Purchase #4	$102.87	8.709%	$111.8289	$111.83	$111.85	$111.80
Purchase #5	$48.53	12.679%	$54.6831	$54.68	$54.70	$54.70
Purchase #6	$50.98	4.430%	$53.2384	$53.24	$53.25	$53.20
Purchase #7	$165.94	13.515%	$188.3668	$188.37	$188.35	$188.40
7 purchase totals =	$814.74		$894.3400	$894.34	$894.40	$894.40