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	$139.43	3.106%	$143.7607	$143.76	$143.75	$143.80
Purchase #2	$228.67	13.415%	$259.3461	$259.35	$259.35	$259.30
Purchase #3	$84.48	6.548%	$90.0118	$90.01	$90.00	$90.00
Purchase #4	$111.39	13.112%	$125.9955	$126.00	$126.00	$126.00
Purchase #5	$188.29	4.246%	$196.2848	$196.28	$196.30	$196.30
Purchase #6	$68.86	4.275%	$71.8038	$71.80	$71.80	$71.80
Purchase #7	$38.58	13.775%	$43.8944	$43.89	$43.90	$43.90
7 purchase totals =	$859.70		$931.0971	$931.09	$931.10	$931.10