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	$29.58	7.276%	$31.7322	$31.73	$31.75	$31.70
Purchase #2	$163.55	7.844%	$176.3789	$176.38	$176.40	$176.40
Purchase #3	$66.28	9.463%	$72.5521	$72.55	$72.55	$72.60
Purchase #4	$41.64	13.521%	$47.2701	$47.27	$47.25	$47.30
Purchase #5	$177.90	6.770%	$189.9438	$189.94	$189.95	$189.90
Purchase #6	$30.28	13.774%	$34.4508	$34.45	$34.45	$34.50
Purchase #7	$106.27	3.423%	$109.9076	$109.91	$109.90	$109.90
7 purchase totals =	$615.50		$662.2355	$662.23	$662.25	$662.30