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	$230.59	9.247%	$251.9127	$251.91	$251.90	$251.90
Purchase #2	$136.92	5.126%	$143.9385	$143.94	$143.95	$143.90
Purchase #3	$236.31	11.251%	$262.8972	$262.90	$262.90	$262.90
Purchase #4	$134.36	7.773%	$144.8038	$144.80	$144.80	$144.80
Purchase #5	$49.63	5.654%	$52.4361	$52.44	$52.45	$52.40
Purchase #6	$137.93	3.146%	$142.2693	$142.27	$142.25	$142.30
Purchase #7	$54.98	7.863%	$59.3031	$59.30	$59.30	$59.30
7 purchase totals =	$980.72		$1,057.5607	$1,057.56	$1,057.55	$1,057.50