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	$164.37	9.768%	$180.4257	$180.43	$180.45	$180.40
Purchase #2	$100.98	5.758%	$106.7944	$106.79	$106.80	$106.80
Purchase #3	$89.42	12.629%	$100.7129	$100.71	$100.70	$100.70
Purchase #4	$242.76	5.343%	$255.7307	$255.73	$255.75	$255.70
Purchase #5	$69.55	12.196%	$78.0323	$78.03	$78.05	$78.00
Purchase #6	$201.87	11.789%	$225.6685	$225.67	$225.65	$225.70
Purchase #7	$25.54	10.264%	$28.1614	$28.16	$28.15	$28.20
7 purchase totals =	$894.49		$975.5259	$975.52	$975.55	$975.50