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	$171.72	3.534%	$177.7886	$177.79	$177.80	$177.80
Purchase #2	$97.39	4.466%	$101.7394	$101.74	$101.75	$101.70
Purchase #3	$113.33	13.164%	$128.2488	$128.25	$128.25	$128.20
Purchase #4	$212.59	8.596%	$230.8642	$230.86	$230.85	$230.90
Purchase #5	$28.30	10.665%	$31.3182	$31.32	$31.30	$31.30
Purchase #6	$92.74	13.511%	$105.2701	$105.27	$105.25	$105.30
Purchase #7	$178.82	6.621%	$190.6597	$190.66	$190.65	$190.70
7 purchase totals =	$894.89		$965.8890	$965.89	$965.85	$965.90