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	$109.25	12.760%	$123.1903	$123.19	$123.20	$123.20
Purchase #2	$60.42	11.786%	$67.5411	$67.54	$67.55	$67.50
Purchase #3	$245.90	9.349%	$268.8892	$268.89	$268.90	$268.90
Purchase #4	$151.44	11.339%	$168.6118	$168.61	$168.60	$168.60
Purchase #5	$127.54	4.849%	$133.7244	$133.72	$133.70	$133.70
Purchase #6	$68.67	7.217%	$73.6259	$73.63	$73.65	$73.60
Purchase #7	$100.80	10.584%	$111.4687	$111.47	$111.45	$111.50
7 purchase totals =	$864.02		$947.0514	$947.05	$947.05	$947.00