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	$66.67	6.525%	$71.0202	$71.02	$71.00	$71.00
Purchase #2	$176.58	4.788%	$185.0347	$185.03	$185.05	$185.00
Purchase #3	$249.83	11.584%	$278.7703	$278.77	$278.75	$278.80
Purchase #4	$145.55	10.198%	$160.3932	$160.39	$160.40	$160.40
Purchase #5	$41.36	4.372%	$43.1683	$43.17	$43.15	$43.20
Purchase #6	$183.89	13.519%	$208.7501	$208.75	$208.75	$208.80
Purchase #7	$249.32	9.849%	$273.8755	$273.88	$273.90	$273.90
7 purchase totals =	$1,113.20		$1,221.0123	$1,221.01	$1,221.00	$1,221.10