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	$127.61	7.407%	$137.0621	$137.06	$137.05	$137.10
Purchase #2	$102.79	10.242%	$113.3178	$113.32	$113.30	$113.30
Purchase #3	$93.97	10.320%	$103.6677	$103.67	$103.65	$103.70
Purchase #4	$111.68	10.534%	$123.4444	$123.44	$123.45	$123.40
Purchase #5	$106.29	12.334%	$119.3998	$119.40	$119.40	$119.40
Purchase #6	$215.55	6.430%	$229.4099	$229.41	$229.40	$229.40
Purchase #7	$154.83	6.272%	$164.5409	$164.54	$164.55	$164.50
7 purchase totals =	$912.72		$990.8426	$990.84	$990.80	$990.80