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	$54.73	12.662%	$61.6599	$61.66	$61.65	$61.70
Purchase #2	$36.64	3.398%	$37.885	$37.89	$37.90	$37.90
Purchase #3	$90.84	11.821%	$101.5782	$101.58	$101.60	$101.60
Purchase #4	$48.95	5.477%	$51.631	$51.63	$51.65	$51.60
Purchase #5	$25.41	11.808%	$28.4104	$28.41	$28.40	$28.40
Purchase #6	$43.28	5.162%	$45.5141	$45.51	$45.50	$45.50
Purchase #7	$226.51	5.814%	$239.6793	$239.68	$239.70	$239.70
7 purchase totals =	$526.36		$566.3579	$566.36	$566.40	$566.40