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	$173.87	6.500%	$185.1716	$185.17	$185.15	$185.20
Purchase #2	$128.51	12.475%	$144.5416	$144.54	$144.55	$144.50
Purchase #3	$175.47	4.254%	$182.9345	$182.93	$182.95	$182.90
Purchase #4	$76.36	7.380%	$81.9954	$82.00	$82.00	$82.00
Purchase #5	$51.82	7.125%	$55.5122	$55.51	$55.50	$55.50
Purchase #6	$142.85	3.211%	$147.4369	$147.44	$147.45	$147.40
Purchase #7	$128.81	11.184%	$143.2161	$143.22	$143.20	$143.20
7 purchase totals =	$877.69		$940.8083	$940.81	$940.80	$940.70