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	$109.92	12.649%	$123.8238	$123.82	$123.80	$123.80
Purchase #2	$114.44	7.643%	$123.1866	$123.19	$123.20	$123.20
Purchase #3	$247.44	10.376%	$273.1144	$273.11	$273.10	$273.10
Purchase #4	$189.49	3.566%	$196.2472	$196.25	$196.25	$196.20
Purchase #5	$244.54	8.661%	$265.7196	$265.72	$265.70	$265.70
Purchase #6	$83.44	5.589%	$88.1035	$88.10	$88.10	$88.10
Purchase #7	$178.64	6.578%	$190.3909	$190.39	$190.40	$190.40
7 purchase totals =	$1,167.91		$1,260.5860	$1,260.58	$1,260.55	$1,260.50