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	$38.27	6.658%	$40.818	$40.82	$40.80	$40.80
Purchase #2	$146.87	3.795%	$152.4437	$152.44	$152.45	$152.40
Purchase #3	$206.62	10.144%	$227.5795	$227.58	$227.60	$227.60
Purchase #4	$247.83	7.142%	$265.53	$265.53	$265.55	$265.50
Purchase #5	$189.51	11.106%	$210.557	$210.56	$210.55	$210.60
Purchase #6	$134.85	7.367%	$144.7844	$144.78	$144.80	$144.80
Purchase #7	$89.87	6.187%	$95.4303	$95.43	$95.45	$95.40
7 purchase totals =	$1,053.82		$1,137.1429	$1,137.14	$1,137.20	$1,137.10