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	$78.99	4.261%	$82.3558	$82.36	$82.35	$82.40
Purchase #2	$28.95	13.581%	$32.8817	$32.88	$32.90	$32.90
Purchase #3	$111.49	7.574%	$119.9343	$119.93	$119.95	$119.90
Purchase #4	$122.64	9.483%	$134.27	$134.27	$134.25	$134.30
Purchase #5	$78.65	4.574%	$82.2475	$82.25	$82.25	$82.20
Purchase #6	$108.66	10.832%	$120.4301	$120.43	$120.45	$120.40
Purchase #7	$188.71	6.374%	$200.7384	$200.74	$200.75	$200.70
7 purchase totals =	$718.09		$772.8578	$772.86	$772.90	$772.80